METHOD AND APPARATUS FOR REPORTING CHANNEL STATE INFORMATION IN
WIRELESS COMMUNICATION SYSTEM
BACKGROUND OF THE INVENTION
The present invention relates to telecommunications apparatus, methods, systems and apparatus
for transmitting data to and/or receiving data from mobile terminals in a wireless communications system.
In particular, the invention relates to reporting of channel state information in wireless communications
systems.
Channel state information may be of particular relevance to the effective operation of machine
type communication (MTC) devices in cellular telecommunications networks having orthogonal
frequency division multiplex (OFDM) based radio access technology (such as WiMAX and LTE).
One of the key issues to be considered in the development of radio technology is fading. Fading
can affect radio propagation in many ways: a receiver may receive multipath signals (taps) which show
the effects of attenuation, time delay and phase shift. In order to overcome fading, link adaptation
techniques are widely used for wireless communication.
In order to use link adaptation, channel state information (such as the channel quality indicator
(CQI) introduced in LTE) needs to be obtained for each UE. CQI is the feedback of a measure of
downlink channel quality from mobile terminal (e.g. user equipment, UE) to base station (e.g. eNodeB).
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method for reporting channel state
information corresponding to a communication link between a terminal device and a base station in a
wireless communications system, the wireless communication system having a system bandwidth divided
into a plurality of sub-band parts having at least one characteristic sub-band size, the method comprising:
providing a plurality of communications resource elements across the system bandwidth;
measuring one or more channel state parameter corresponding to the channel state in one or more
of the communications resource elements;
generating aggregate channel state information from at least one measured channel state
parameter corresponding to the channel state of the communications resource elements,
generating sub-band channel state information from at least one measured channel state
parameter corresponding to the channel state of the communications resource elements within respective
sub-band parts,
wherein the size of the sub-band part is dependent upon radio propagation conditions.
The channel state information may preferably be a channel quality indicator (CQI). As a result,
sub-band size is altered depending on the degree of the channel quality fluctuation in frequency domain
(e.g. subcarrier or RBs). When the channel is flat, large sub-band size (max case wideband CQI) is
selected.
Conveniently, the plurality of sub-band parts may have a plurality of characteristic sub-band
sizes, at least a first group of the sub-band parts having a first characteristic sub-band size and a second
group of the sub-band parts having a second characteristic sub-band size, the first characteristic sub-band
size and second characteristic sub-band size being different, thereby facilitating reporting channel state
information at different degrees of granularity for different parts of the system bandwidth. Thus within a
(wide band) host carrier, the sub-band size is adaptively selected depending on fluctuation of channel
quality.
This makes it possible to provide fine resolution frequency scheduling and better performance of
throughput for narrowband carriers and allows an efficient MTC Virtual carrier (narrow band) operation
in host carrier.
Furthermore the method facilitates the indication of the sub-band size that has been configured.
As a result of the method, the sub-band size is preferably selected in dependence on the presence
and degree of frequency selective fading.
The method provides not only wideband CQI, but also fine resolution sub-band CQI for
narrowband carriers such as the virtual carrier subsystem described below.
Various further aspects and embodiments of the invention are provided in the accompanying
independent and dependent claims.
It will be appreciated that features and aspects of the invention described above in relation to the
first and other aspects of the invention are equally applicable to, and may be combined with,
embodiments of the invention according to the different aspects of the invention as appropriate, and not
just in the specific combinations described above. Furthermore features of the dependent claims may be
combined with features of the independent claims in combinations other than those explicitly set out in
the claims.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present invention will now be described by way of example only with
reference to the accompanying drawings, where like parts are provided with corresponding reference
numerals and in which:
Figure 1 illustrates schematically certain functional elements of a conventional mobile
telecommunications network;
Figure 2 shows the conventional selection of the "Best M" sub-band CQIs;
Figure 3 illustrates an exemplary UE initiated semi-static sub-band size configuration procedure
in accordance with a second embodiment of the invention;
Figure 4A to 4C illustrate exemplary eNodeB initiated semi-static sub-band size configuration
procedures in accordance with the second embodiment of the invention;
Figure 5 illustrates the subcarrier SINR method for determining the sub-band size change in
accordance with an embodiment of the invention;
Figure 6 illustrates how sub-band size calculation window is changed during sub-band size search
in the subcarrier SINR method;
Figure 7 shows a plurality of sub-band CQIs each being prepared for direct transmission for each
sub-band;
Figure 8 shows an alternative method for transmitting the sub-band CQIs using time division;
Figure 9 illustrates a selected sub-band CQI report method (which only reports CQIs if they fall
out of a predetermined range);
Figure 10 illustrates LI sub-band CQI reporting;
Figures 1A to 1 C illustrate different types of signalling in the physical layer (LI) for sub-band
size signalling;
Figure illustrates the UE initiated sub-band size change procedure (using RC);
Figure 13 illustrates an eNodeB initiated sub-band size change procedure (using RRC);
Figure 14 illustrates MTC server initiated sub-band size change procedure;
Figure 15 schematically represents the functional constituent blocks within a typical terminal
(UE);
Figure 16 illustrates the logical architecture of the baseband processing elements of a terminal;
Figure 17 schematically represents the functional constituent blocks within atypical eNodeB;
Figure 18 illustrates the logical architecture of the baseband processing elements of a base
station;
Figure 1 illustrates the protocol stack for an LTE/SAE/MTC architecture;
Figure 20 shows a virtual carrier coexisting in a host carrier
Figure 2 1A illustrates frequency selective fading (of channel quality);
Figure 2 1B illustrates the adaptive sub-band size across a range of frequencies in frequency
selective fading conditions;
Figure 22 illustrates the power delay profile for a multipath signal having a plurality of taps; and
Figure 23 illustrates a typical power delay profile averaged over a plurality of multipath signals.
DETAILED DESCRIPTION
Figure 1 provides a schematic diagram illustrating some basic functionality of a conventional
mobile telecommunications network, using for example Long Term Evolution (LTE) architecture.
The network includes a plurality of base stations 4 (only one is shown for simplicity)
connected to a core network 110 (in dotted box). Each base station 104 provides a coverage area (i.e. a
cell) within which data can be communicated to and from terminal devices (also referred to as mobile
terminals, MT or User equipment, UE) 102. Data is transmitted from base stations 104 to terminal
devices 102 within their respective coverage areas via a radio downlink 124. Data is transmitted from
terminal devices 102 to the base stations 104 via a radio uplink 122.
The core network 110 routes data to and from the terminal devices 102 via the respective base
stations 104 and provides functions such as authentication, mobility management, charging and so on.
Typical entities in a core network include a Mobility Management Entity, MME, 106 and a subscriber
database (IISS) 108: these entities facilitate the provision of communications services to UEs wherever
they are located within the coverage of the network. Access to data services is provided by a serving
gateway 112 and a packet data network, PDN, gateway 114.
Figure 1 also shows elements which extend the network to allow efficient management of
machine type communication (MTC) devices. The illustrated core network 110 incorporates an MTC
server 116. An optional MTC gateway 120 is also shown in Figure 1: such a gateway may provide a hub
terminal device which is in communication with one or more MTC devices and in turn establishes uplink
and/or downlink communication paths with the base stations 104 on behalf of the connected MTC
devices.
Throughout this disclosure, the term "MTC server" refers to an MTC server of the type defined in
3GPP TS 22.368 [1]: the definition there being of a server, which communicates to a public land mobile
network (PLMN) [i.e. a mobile telecommunications network] and to MTC Devices through the PLMN.
The MTC Server also has an interface which can be accessed by the MTC User. The MTC Server
performs services for the MTC User.
In mobile telecommunications systems such as those arranged in accordance with the 3GPP
defined Long Term Evolution (LTE) architecture, communication between base stations (e.g. eNodeB
104) and communications terminals (e.g. UE 102, MTC gateway 120) is conducted over a wireless airinterface,
Uu. Downlink 124 on the Uu interface uses an orthogonal frequency division multiple access
(OFDMA) technology, while uplink 122 uses single carrier frequency division multiple access (SCFDMA)
technology. In both cases, the system bandwidth is divided into a plurality of "subcarriers" (each
occupying 15 kHz).
The downlink Uu interface organises resources in time using a "frame" structure. A downlink
radio frame is transmitted from an e ode B and lasts 10 ms. The downlink radio frame comprises ten
subframes, each subframe lasting 1 ms. The subframe in turn comprises a predetermined number of
"symbols", which are each transmitted over a respective 1/14 ms period. Each symbol comprises a
predetermined number of orthogonal subcarriers distributed across the bandwidth of the downlink radio
carrier.
To take a specific example, a subframe may be defined to have 14 symbols and 1200 subcarriers
spread across a 20MHz bandwidth. User data is allocated for transmission by the scheduler of the
eNodeB in "resource blocks" (RB) comprising twelve subcarriers.
When compared with serial data transmission techniques, OFDM techniques are considered to be
tolerant of delay spread as a consequence of the comparatively long time duration of the symbols.
Nevertheless, there are circumstances when this tolerance is insufficient.
Over the time scales of OFDM signals, fading in the frequency domain can be relatively flat.
Frequency selective fading does arise where cells are relatively large and/or cover certain disruptive
features in the natural or built environment: a cell covering a large dense urban district with a high
proportion of mobile UEs would typically experience greater delay spread than a cell covering a sparsely
populated plain. In order to overcome fading, link adaptation techniques are widely used for wireless
communication.
In order to use link adaptation, channel state information (such as the channel quality indicator
(CQI) introduced in LTE) needs to be obtained for each UE. CQI is the feedback of a measure of
downlink channel quality from mobile terminal (e.g. user equipment, UE) to base station (e.g. eNodeB).
Coherence bandwidth and delay spread
Excessive delay may impact on ISI (Inter-symbol-interference) and it may cause frequency
selective fading.
For a multipath signal, an example power delay profile might look like Figure 22. Here, the
power in a received signal, P(t), is received as N(=4) taps: Pi(t) to P (t).
In the literature, the term "excess delay" is the delay of any tap relative to the first tap. Likewise,
the term "total delay" is the delay difference between first and last tap.
Total power, P is the sum of all the tap powers, i.e.
Mean delay, t , is defined as the average delay weighted by power
One of the key parameters for wireless propagation characteristics is the delay spread. Delay
spread is a standard deviation (or root-mean-square, r.m.s.) value of the averaged multipath delay. The
root mean squared (rms) delay spread, t , is in turn defined using the concept of the mean delay, as
follows:
" =1
As the rms delay spread is a characteristic that can be calculated in many different radio
conditions, the rms delay spread is used to allow comparison of various environments.
When one considers a plurality of power delay profiles, the averaged power delay profile might
look like Figure 23. The terms defined above are essentially the same in the treatment of averaged data.
RMS delay spread can thus show the statistical distribution of delays which is caused by
multipath. A large delay spread correlates to frequency selective fading in wide-band systems (see Figure
2 1A). A relatively small delay spread by contrast corresponds to a "flat fading" profile, where fading is
relatively independent of frequency across the system frequency bandwidth.
To derive an expression for delay spread, it is helpful, first, to define an expression for the
weighted average multipath delay:
1 t
D = °) P d P d
in which P is power; tx is the delay of a given multipath x; t is the delay; and Papd is an
expression for the average power delay profile (See Figure 23). As for the discrete case, illustrated in
Figure 22, the RMS delay spread, Dspread, may be defined using the weighted average multipath delay.
The frequency selective fading in channel quality illustrated in Figure 21A includes ranges of
frequencies over which the fading in channel quality remains flat (2102, 2104) and other ranges at which
fading is more pronounced (2106, 2108). Noteably, a flat fading profile is not necessarily correspond to a
high channel quality measure, as is the case for one illustrated range 2102; where channel quality is
relatively low but fading is not frequency selective over that range.
In order to simplify evaluation of the fading characteristic (for direct comparison to system
bandwidth, for example), "coherence bandwidth" may be calculated from delay spread. The coherence
bandwidth, Wc, for a given system is defined in the following formula:
1
Wc =
p ' ad
where, D means the delay spread.
For a system having a known system bandwidth (e.g. 20MHz), the coherence bandwidth is used
to determine whether the delay causes flat fading or frequency selective fading. If coherence bandwidth
is wider than system bandwidth, it is flat fading. If coherence bandwidth is narrower than system
bandwidth, it is frequency selective fading.
In the case of LTE, the delay spread is determined by consulting a table reproduced here as Table
1, quoted from R4-070572 submission to 3GPP. Table 1 Summary of delay profiles for LTE channel
models.
In urban macro area with Macro-cell, the larger delay spread might be considered most likely to
occur. For example, Winner project defined the delay profile for wide area between 10ns and 4600ns -
further details of the Winner project may be found at http://projects.celtic-initiative.org/winner+.
CQI Report
In order to provide accurate link adaptation, a channel quality indicator (CQI) was introduced in
release 8 of LTE. UE measures the channel quality of the downlink and reports it to an eNodeB (in an
uplink transmission, e.g. PUSCH or PUCCH). CQI is used to report a measure of the channel quality of
the downlink. Based on the report, the eNodeB performs link adaptation by means of a scheduler.
Two categories of CQI are defined, one is periodic CQI and the other is aperiodic CQI. UE
transmit periodic CQI for every certain subframe. The certain subframe can be changeable by higher
layer if necessary. UE also transmit aperiodic CQI if necessary.
Furthermore two bandwidth types of CQI are considered: one is wideband CQI, the other is subband
CQI. Due to frequency selective fading, the channel quality of each subcarrier might be different.
In the case of wideband CQI, one value, averaged over the whole bandwidth, is transmitted. Wideband
CQI reports do not assist in adapting to frequency selective situations. In the case of sub-band CQI, the
whole band is split into sub-band parts and the channel quality of each sub-band part is measured.
Comparing coherence bandwidth with system bandwidth in wideband systems, like LTE, it is
clear that the wider system bandwidth leads to a higher predisposition to suffer frequency selective
fading. The sub-band CQI thus provides a more responsive frequency scheduling than the wideband CQI
alone.
Sub-band Size
order to avoid requiring an excessive number of sub-band CQI transmissions, the sub-band
size is selected to be a limited number of resource blocks. Depending on system bandwidth (whole
bandwidth), the sub-band size is defined in the specification (see Table 2), where parameter Sub-band
Size k is the number of RBs (Resource blocks).
Table 2 Sub-band Size (A) vs. System Bandwidth
(From 3GPP TS 36.213 V8.8.0)
In its present specification, therefore, the LTE standard provides no definition of sub-band CQI in
LTE systems having system bandwidth of narrow band (e.g. less than or equal to 6RBs). Only wideband
CQI is applied for this case. It is noted that, in this specification, all but the sub-band at the highest
frequency will be of the same, defined sub-band size.
"Best M" sub-band CQI transmission
Even if the sub-band size is defined more to be than one RB (Resource Block), the number of
CQI which UE have to transmit at one time is typically considered too large. For example, when the
system bandwidth is 110 RBs (20MHz), the number of sub-bands is 110/8 = 13. In order to reduce the
signalling load and uplink interference, a CQI reporting method is introduced in REL-8 LTE which
selects a restricted number, M, of CQI from amongst the plurality of CQIs measured by the UE. The
scheduler operates to allocate the frequency resource of good condition for UE, so it is more important for
the scheduler to know which sub-band is in "best condition" rather than which one is worst condition.
Therefore, UE makes the ranking based on sub-band channel quality and select the best "one to
Mth" sub-band CQIs and transmits the selected sub-band CQIs.
In the example illustrated in Figure 2, the UE is configured to report only the "best two" CQIs:
the UE transmits the "best" sub-band CQI value 202 and "second best" sub-band CQI value 204 on top of
wideband CQI value. The CQI is omitted for other sub-bands 206 from third best-to Mth best. This
method reduces unnecessary signalling.
CQI difference transmission method
If the absolute value of CQI is transmitted for each sub-band, the number of signalling bits to be
transmitted may be large because the signalling load is the number of sub-band multiplied by the value of
CQI granularity (i.e. the number of quantization bits).
In order to reduce the signalling overhead, a difference transmission method is introduced in
REL-8 LTE. In other words, the sub-band CQI is transmitted as a difference value between the measured
sub-band CQI and the prevailing wideband CQI; thereby reducing the number of bits to be transmitted.
Sub-band CQI = wideband CQI (whole band) + difference value (sub-band)
Sub-band CQ for narrowband
As has been noted above, particularly with reference to Table 2, sub-band size is not defined in
all conventional LTE systems: the LTE standard provides no definition of sub-band CQI in LTE systems
having system bandwidth less than or equal to 6RBs (referred to hereafter as "narrowband" systems), h
these narrowband systems, only wideband CQI are applied. This has not been considered to be a
particular issue before, because most network operators have allocated more than 6RBs (e.g. 5MHz or
wider) of bandwidth to LTE; the 6RB case, while provided for in the standard, is not common.
However, there are scenarios, for instance an urban area with a large cell (and therefore a
presumed delay spread of 3000ns-4000ns), where finer frequency resolution may be attractive in spite of
the narrower system bandwidth.
In particular, the terminal may use narrow band (i.e. "virtual carrier") rather than wideband to
support effective MTC device operation. The standard specification does not necessarily cater for this
situation very well.
Previous co-pending patent applications have discussed in detail the design and operation of some
parts of a so-called virtual carrier (VC) subsystem, embedded in a conventional host carrier (HC), suitable
for use particularly in LTE networks serving machine-type communication (MTC) devices among their
mix of user equipment terminals (UEs). Certain aspects of virtual carrier systems are discussed in Annex
1 below.
To adapt conventional CQI reporting to the circumstances where narrowband systems, and MTCsupporting
virtual carrier systems in particular, need sub-band CQI, three related methods for defining
and if necessary adapting a sub-band size are described: fixed, semi-static and adaptive sub-band size. To
varying degrees, they are each specified in accordance with the channel condition.
The selection of a new sub-band size may not be straightforward as, depending on the situation of
the UE (Urban area, macro-cell etc.) the delay profile may be different. This situation may however be
used for pre-configuration of sub-band size.
One of the key benefits of OFDM based radio technologies (such as LTE) is frequency
scheduling. However, wide-band CQI cannot deliver this benefit alone. Sub-band CQI reporting
supplements the wideband CQI to give finer measurement of the radio conditions in any given sub-band
so that this can be taken into account by the scheduler.
The MTC devices using a narrowband carrier can experience selective fading in case of large
delay profiles (e.g. urban area).
Preferably, new sub-band size which is optimized for MTC operation should be defined for
virtual carrier.
The various embodiments introduce a sub-band size for a VC subsystem (where none was
provided previously) and at least one embodiment introduces an "adaptive sub-band size".
Specific embodiments are described in the following order:
A first embodiment in which a fixed sub-band size is defined for a narrow band of 6RB or less.
A further finer sub-band size is considered on the basis of individual subcarriers within resource blocks.
A second embodiment in which a semi-static sub-band size is defined. By semi-static is meant
that the sub-band size, once defined - upon installation of MTC device, for instance, is seldom if ever
changed but permits changes should this be desired
A third embodiment in which the concept of adaptive sub-band size, i.e. the definition of subband
size in accordance with substantially current channel condition in the narrow system frequency band
of a virtual carrier.
Thereafter the details of suitable CQI transmission methods are described.
Additional techniques for physical and higher layer signalling of VC sub-band configuration are
also then set out.
Fixed sub-band size for virtual carrier (Embodiment 1)
In this embodiment, a new sub-band size is introduced in case of narrow band (e.g. 6RBs
bandwidth).
A convenient and suitable size of frequency range for this narrow band sub-band is a B ( 1
resource block = * 15kHz = 180 kHz), which is the baseline of resource allocation in LTE. As a
result, for a virtual carrier bandwidth of 6RBs, this would give six sub-bands.
In one version of the fixed sub-band size case, this sub-band size may be defined in a table (Table
3). The benefit of fixed size and defined in specification is that there is no need for signalling.
Table 3 the fixed sub-band size definition (examples)
In a typical urban environment (e.g. delay profile = 000ns), 1RB resolution might be sufficient.
However, if larger delay profile (2000-5000ns, i.e. complicated multipath case), a finer resolution might
be better. As Table 3 indicates, if the finer resolution is needed, a sub-band size of one subcarrier can be
used (there are 12x6=72 subcarriers for 6RBs).
Table 3 shows examples of suitable fixed sub-band size. There are of course other alternatives,
for instance an intermediate case (e.g. 2RBs) is also possible.
The procedure of sub-band CQI transmission in MTC
An exemplary procedure for sub-band CQI transmission, suitable for implementation in an MTC
terminal using a narrowband (VC) subsystem, includes: measurement of channel characteristics within
each VC sub-band (for example, signal strength, interference, etc.); calculation of signal to interference
plus noise ratio (SIN ); averaging the SINR results for each VC sub-band of a fixed sub-band size;
optionally, selecting the "best M" VC sub-band CQI values; performing coding and modulation;
allocating physical resources for the selected sub-band CQI values and wideband CQI value; waiting for
the next subframe to transmit selected sub-band CQI (periodic case) and/or transmitting selected sub-band
CQI to eNodeB (both periodic and aperiodic reporting cases); and waiting for the scheduling information.
A suitable exemplary counterpart procedure to the above procedure for sub-band CQI
transmission in base station includes: waiting for the subframe for CQI (periodic case only); receiving
the sub-band and wideband CQI; performing demodulation and chamiel decoding; reading CQI value and
input to scheduler; and scheduling transmissions. Scheduling transmissions includes: selecting a
Modulation and Coding Scheme (MCS) based on CQI values; indicating downlink (DL) resource
allocation on PDCCH; transmission of data on PDSCH; receiving ACK/NACK from UE; and
retransmitting data, if necessary (e.g. if NACK received or time out without ACK or NACK).
Semi-static sub-band size for virtual carrier (Embodiment 2)
In another embodiment, a semi-static configuration may be applied to the determination of a
suitable sub-band size.
Semi-static means once the sub-band size is decided, it continues to be used until the situation is
changed. For example, in case of smart meter, the value is configured at the meter install, there being no
need to change the size after that under typical conditions. In general, if the MTC terminal is fixed or
unlikely to move (e.g. smart meter), the sub-band size will not need to be changed often. The semi-static
configuration method is also suitable for cases where a UE (not necessarily an MTC device) is stationary.
Compared to embodiment 1, the semi-static configuration of sub-band size needs to be aligned at
least once between UE and eNodeB.
One simple way of defining sub-bands in these circumstances is to provide a parameter which has
direct value of sub-band size. This is simple and adaptable to any case.
If there are a limited number of options for sub-band size, it may alternatively be effective to
define sub-band size with reference to a table. Table 4 shows an exemplary configuration of sub-band
size for semi static case. Depending on configuration number, sub-band size k is defined. In this case, the
number of signalling for indication of sub-band size might be reduced compared to direct value.
Table 4
The procedure of semi-static sub-band size configuration
Two cases of semi-static configuration are considered: one is UE initiated (UE decides
appropriate sub-band size or stores pre-configuration and indicates this to the eNodeB); the other, is
eNodeB initiated (eNodeB decides an appropriate sub-band size or stores a pre-configuration for a certain
UE and indicates this to the UE).
In UE initiated case, based on manual input, terminal may send the signalling of sub-band
configuration with higher layer to eNodeB. Alternatively it is configured for UE in advance (as an initial
setting).
The sub-band size can be configured based on parameters selected individually or in combination
from the following categories of radio propagation conditions:
• a site type or characteristic cell radius which covers the MTC UE: examples of site types include:
macro-cell, micro-cell, pico-cell, femto-cell (such as provided by an indoor, consumer-installed base
station unit). As noted above, a macro-cell may experience greater delay spread and a smaller subband
size would be warranted.
· Morphology of area (considerations here include: whether the area is hilly or mountainous; whether it
is close to an expanse of water; or the nature of the built environment ) - examples of types of
morphologies include: dense urban, urban, sub-urban, and/or rural
• Mobility type of UE (Fixed, slow, middle, high). High mobility, a UE in a car travelling at 100km
per hour, for instance, might mean that local conditions giving rise to selective frequency fading
would be transitory and wideband CQI might be adequate, whereas a smaller sub-band size may be
useful for a static or slow moving UE under such conditions.
• UE Type (mobile handset, smart meter, hub/gateway device, home appliance etc.)
• Location of UE (e.g. map reference, GPS Area name, City name etc,): a database of geographic
locations (indexed by grid reference, GPS coordinates or other suitable scheme) may be provided
which associates a location to an expected delay profile (so that "Boulder, CO" would be associated
with a higher expected delay profile than "Amagansett, Long Island, NY").
• Direct value (e.g. delay profile, delay spread, system bandwidth, transmission mode etc.)
Figure 3 illustrates an exemplary UE initiated semi-static sub-band size configuration procedure.
Firstly, an external maintenance terminal 330 pre-configures a UE 302 to facilitate setting (and local
storage 318) of a semi-static sub-band size value (or table of values) - step S320. The UE 302 is
initialised and sends the semi-static sub-band configuration to an eNodeB 304 (so that the eNodeB can
interpret CQI reports from that UE) - step S322. The sub-band configuration sent by the UE 302 may
include for example radio bearer setup data. In one implementation, the UE 302 is an MTC device and
the sub-band configuration is sent under control of an MTC server 316. Completion of configuration is
confirmed by receipt of a completion message from the eNodeB 304 - step S324.
In the eNodeB initiated case, based on location information (e.g. GPS location, geographic
coordinates), the eNodeB can estimate radio environment (Urban, rural, etc.) and the delay profile for
each UE. Based on this, the eNodeB decides upon the sub-band size and indicates the selected sub-band
size to UE.
Figure 4A illustrates an exemplary eNodeB initiated semi-static sub-band size configuration
procedure. Here a eNodeB 404 obtains information of cell situation (location information etc.) S432,
sends the semi-static sub-band configuration to a UE 402 (as part of radio bearer re-configuration
signalling, for example) S434 and once the UE 402 completes initialisation, receives a completion
message from UE 402, S436.
Figure 4B illustrates another exemplary eNodeB initiated semi-static sub-band size configuration
procedure. In addition to retrieving default eNodeB parameter settings S440, the eNodeB 404' obtains
information of cell situation (location mformation etc.) S442 and sends the semi-static sub-band broadcast
information to a UE 402' (as part of MGB/SEB, for example) S444. Once the UE 402' receives this
information, the UE 402' configures itself S446. h this example, the UE 402' sends no completion
message. Thus sub-band size may be configured according to default eNodeB parameter settings.
It is contemplated that MTC devices may be provided with limited flexibility in terms of subband
sizes that can be adopted. Figure 4C illustrates another exemplary eNodeB initiated semi-static subband
size configuration procedure suitable where UEs might have a restriction of capability (i.e. the
selection of sub-band size is not flexible due to lack of UE capability). Flere a first eNodeB 404" obtains
information of cell situation (location information etc.) S450, sends the semi-static sub-band size
information to a UE 402" (as part of MTB/SIB, for example) S460 and once the UE 402" receives this
information, the UE 402" checks whether it is acceptable or not (i.e. the UE can report using the subband
size indicated in the broadcast information) S462.
If the sub-band size is determined not to be compatible, the UE 402" seeks attachment to another
cell (i.e. reselection) and the procedure starts again S464. Thus a second eNodeB 454 obtains information
of cell situation (location information etc.) S452, sends a second semi-static sub-band broadcast
information to the UE 402" (as part of MIB/SIB, for example) S466 and once the UE 402" receives this
information, the UE 402" checks whether it is acceptable or not (i.e. the UE can report using the subband
size indicated in the broadcast information) S468. In this second case, the UE 402" finds an
eNodeB 454 offering a compatible sub-band size. The UE 402" decides to use this cell and configures
the sub-band size accordingly S470.
Adaptive sub-band size for virtual carrier (Embodiment 3)
n the third embodiment, the preferable sub-band size depends on characteristics of propagation
environment, typically time-varying.
Three sub-band size selection methods are considered: the "delay spread" method; the "subcarrier
SBNR" method; and a method based on PDSCH Tx mode. Each adapts the recommended sub-band size to
suit the time-varying ambient radio propagation environment.
Based on time domain measurement (the delay spread)
The "delay spread" method directly estimates the coherence bandwidth from delay spread by
measurement.
As noted above, delay spread is the root-mean-square value of the weighted average multipath
delay. In providing a channel estimation function, the UE receiver finds the multipath and averages the
strength and time dispersion. Based on this value, the coherence bandwidth is calculated and a suitable
sub-band size is selected depending upon the inferred fading conditions (i.e. whether there is flat or
frequency selective fading).
The UE performs the channel estimation and synchronization based on reference signals from
eNodeB, the frequency response of each channel is obtained by channel estimation and then converted
from frequency domain to time domain.
In time domain signal, each multi-path of timing and power is obtained. By averaging them, the
delay spread can be calculated.
The steps of sub-band size selection from delay profile include:
• Channel estimation: in which channel coefficients are obtained (frequency response)
• Inverse fast Fourier transform (IFFT), in which the channel coefficients are converted from frequency
domain to time domain
• Calculate; weighted average of multipath delay
D = - t0) Papd dp d
where
• Calculate delay spread
spr ad = standard deviation (averaged delay)
· Calculate coherence bandwidth
Wc =
• IF (coherence bandwidth < the current sub-band size) THEN select smaller sub-band size
• (coherence bandwidth > the current sub-band size) THEN select larger sub-band size
« ELSE IF (coherence bandwidth ~ the current sub-band size) THEN keep the current sub-band
size.
» Indicate the preferable sub-band size to eNodeB. Techniques for signalling adaptive sub-band
size changes are discussed below.
Based on frequency domain measurement (subcarrier SINR)
The second sub-band size selection method uses frequency domain measurements for each
subcarrier. This method is based on signal to interference plus noise ratio (SINR) measurement and
evaluate the fluctuate of SENR for each subcarrier (or each RBs), in essence this method determines the
sub-band size by determining:
IF (the difference of average SINR between sub-bands [510, 512] > threshold X), THEN different
sub-band is allocated.
The sub-band size change, based on subcarrier SINR, is illustrated in Figure 5. For each
successive sub-band (sub-band 3, 503, say) the average STNR is compared to the previous value for
average SENR (sub-band 2, 502, in this example) and if the difference, 512, exceeds the threshold
difference, X, triggers a sub-band size selection procedure.
The steps of sub-band size selection from subcarrier SENR include:
• Measurement of SENR for frequency domain (i.e. each subcarrier/RBs)
• Assume the tentative sub-band size X =2
• Sub-band size search (described below)
• Indicate the preferable sub-band size to eNodeB. Again, techniques for signalling adaptive subband
size changes are discussed below.
Sub-band size search procedure
The large sub-band size should preferably be selected for little fluctuation of channel quality,
whereas narrow sub-band size should be selected for large fluctuation of channel quality.
The sub-band search procedure introduces a "calculation window" for sub-band size selection, as
illustrated in Figure 6. The standard deviation of the channel quality is calculated for the SENR
measurements in the window. The standard deviation of channel quality shows the degree of CQI
fluctuation in the window.
If the standard deviation is below a pre-defined threshold, the channel quality in the window
could be flat and the sub-band size is left unchanged.
If the standard deviation is above the defined threshold, this would indicate that the channel
quality in the window was not flat. An incrementally narrower sub-band size is tried in the next stage
(shown as the shorter "windows" in "stage 2" of Figure 6).
The steps of sub-band size search include:
. Define the initial calculation window size (sub-band size)
2. Calculation start
3. Set the calculation window between the start position and end position( start position + sub-band size)
o Calculate the standard deviation of CQI
o Store the standard deviation
o Shift window start position one B higher (in frequency)
o Repeat until the end position reached (i.e. the band edge)
4. Search for the value below the threshold (e.g. threshold is 1.414 if tolerance is ±2) among the stored
standard deviation values.
5. Select the sub-band size and the range ( between start position and end position)
6. Stage 2 start ( new sub-band size for remaining part)
7. Set new calculation window size ( previous size - 1 RB)
o Repeat from 2 to 5
o If the sub-band size=l RB then end; else go to 7
The resulting ranges of sub-bands have sub-band sizes tailored to the more local fading
characteristics as illustrated in Figure 21B.
Rather than exiting the procedure above [i.e. "end"], in certain embodiments the procedure moves
on to a next frequency range. For system bandwidths, or ranges of bandwidth within the system
bandwidth, where frequency selective fading is flat the sub-band size may stay the same or be allowed to
increase; conversely where the frequency selective fading is more profound, the sub-band size in that
system bandwidth or range of bandwidths is progressively reduced.
Based on PDSCH Tx mode
The third sub-band size selection method infers the appropriate sub-band size from the PDSCH
transmission (Tx) modes being used in the downlink.
There are many diversity techniques to overcome fading. Multi-antenna techniques have proven
particularly effective these are represented as distinct Tx modes.
For example in case of PDSCH Tx mode 2, which is Tx diversity (SFBC), wideband CQI may be
applied. On the other hand Tx mode , which is single port, sub-band CQI is applied.
Another example, in case of PDSCH Tx mode 9, which is Dual layer beamforming, wideband
CQI is applied, because beamforming may save the fading.
Depending on PDSCH Tx mode, it is possible to select a sub-band size automatically. This is socalled
implicit signalling (because the selected size is inferred without being explicitly signalled).
CQI transmission method
Once a sub-band size has been determined according to any one of the embodiments of the
invention described above, the resulting sub-band CQIs need to be transmitted efficiently to the eNodeB.
CQI transmission may be achieved using a variety of methods including: direct transmission for each subband
(where each of the techniques for transmitting CQIs discussed above may be adopted: transmitting
each sub-band CQI directly or transmitting the sub-band CQI as difference values relative to a wideband
CQI). In certain circumstances sub-band CQIs can be transmitted at different times a technique referred
to as time division CQI reporting. The "M best" technique may also be adopted to transmit selected subband
CQIs. In addition, it may not be necessary to transmit any CQI where conditions are appropriate -
the conditions may suitably be defined by the eNodeB.
Direct transmission
The best way of CQI transmission is to transmit all the sub-band CQI values at the same timing,
if signalling load can be allowed. This is illustrated in Figure 7. For example, if sub-band CQI (at fine
resolution) uses 4 bits and the bandwidth is set at 6RBs (giving six sub-bands, 704-1, ... 704-6), the total
signalling load 702 is 4x6=24 bits.
h EL8, only the wide-band CQI can be used at 4 bit resolution, but in narrowband (e.g. VC),
the signalling load from this direct method may be acceptable.
However, if the number of sub-bands is large, the signalling load may increase beyond an
acceptable level. The differential CQI method (described above) might be applied for this case. Thus for
a Wideband CQI of 4 bits and six 2 bit Sub-band difference values (2x6=12 bits), the total number of bits
transmitted = 4+12=16 bits.
Depending on the number of sub-bands (or sub-band size), direct transmission and differential
transmission might be interchanged.
Time division transmission
An alternative method is to transmit respective sub-band CQI values 804, 804' in different time
slots (time =l,time =2, etc.). This is illustrated in Figure 8.
MTC terminal might be fixed (e.g. smart meter), in that case, the variation of value might be not
change significantly over time. In that case, time division CQI transmission might be used without
detrimental effect. As this would result in a signalling load 802, 802' of say 4 bits per sub-band CQI at
one time, this serves to reduce the signalling load and avoid uplink interference.
Selected sub-band transmission
If the sub-band CQI is near to average value 910, there may be no need to send every sub-band
CQI. In the selected sub-band transmission method, the CQI transmission is omitted provided the subband
CQI value remains within a certain range. This is illustrated in Figure 9. An exemplary scheme
may include the following steps:
• Obtain wideband CQI 9 0 (averaged over system bandwidth)
• Define an upper boundary, 902 = wideband + threshold X ( or direct signalling)
• Define a lower boundary, 904 = wideband - threshold X ( or direct signalling)
« Obtain each sub-band CQI value
· IF the sub-band CQI > upper boundary THEN Transmit the sub-band CQI (not shown)
• IF the sub-band CQI < lower boundary THEN Transmit the sub-band CQI (906)
The signalling of adaptive sub-band change
There are two classes of signalling for sub-band size change: LI signalling may be used for fast
changing case, while RRC may be used for slow changing case.
• LI signalling (fast)
• All sub-band
Selected sub-band
Variable sub-band size
RRC signalling (slow)
• UE initiated
• eNodeB initiated
• application ( MTC server) initiated
LI signalling of sub-band size change
If the sub-band size is changed quickly, the best way of signalling is using physical layer (layerl).
This is called LI signalling. A portion of each subframe of the radio frames is dedicated to the
transmission of L I signalling.
In Figure 10, the L I signalling is used to transmit sub-band size changes periodically and/or
aperiodically from UE 1002 to eNodeB 1004 (S1020,S1020,S1030). The LI signalling may be related
variously to the change of sub-band size for all sub-bands; for a selection of sub-bands or even to allow
for the sub-band size to vary for different groups of sub-bands.
In the all sub-bands case, illustrated in Figure 11A, sub-band size changes relate to all sub-bands
equally. It is noted that, if sub-band size is fixed or semi-static and sub-band CQIs are reported for all
sub-band parts, the only information that needs to be transmitted is the sub-band CQI 1102, 1104, 1106.
For fixed or semi-static sub-band sizes, the signalling of sub-band sizes need not be included at all.
In the selected sub-bands case, illustrated in Figure 11B, sub-band size changes are transmitted
for selected sub-bands. If sub-band size is fixed or semi-static and only selected sub-bands are
transmitted, both selected sub-band number 1112, 1116 and the value of CQI at selected sub-band 1114,
1 1 18 should be transmitted.
In the variable sub-band size case, illustrated in Figure 11C, CQI transmission needs to convey
each of the sub-band sizes for each of the respective sub-band CQIs reported. If sub-band size is
dynamically changed, and selected sub-band CQIs are transmitted, the selected sub-band number
1122,1 132, the corresponding size for the selected sub-band 1124, 1134 and the value of CQI at selected
sub-band 6, 1136 should each be transmitted. Clearly this last technique will require a considerably
larger signalling payload than the preceding techniques.
Figure 21B shows variable sub-band size across different ranges of bandwidths within a system
bandwidth. Thus if sub-band CQI values are to be signalled for sub-bands 2110 and 2 112, the position of
the respective sub-bands and their corresponding sizes will be reported along with the CQI value itself.
RRC signalling of sub-band size change
UE initiated RRC signalling
In UE initiated case, illustrated in Figure 12, a UE 1202 measures and decides the preferable size
of sub-band, and requests this from an eNodeB 1204. The signalling is via RRC (e.g. Measurement
report) and includes the following steps: measurement at UE 1202 (S1210); selection of sub-band size
(S1212); transmission of change request of sub-band size (S1214); receipt of sub-band size configuration
(S1216); and optionally transmission of a "reconfiguration complete" message (S1218).
RRC signalling/eNodeB initiated
In eNodeB initiated case, illustrated in Figure 13, an UE 1302 reports the sub-band CQI and an
eNodeB 1304 stores the values. The eNodeB includes a scheduler 1350, which decides which modulation
and coding scheme (MCS) to apply and sends downlink packets to UE 1302.
The scheduler 1350 at eNodeB receives an indication of the success (or otherwise) of the
decoding of these download packets via ACK/NACK (S1318). Based on these, the scheduler 1350
decides the preferable sub-band size.
Via RRC (e.g. physical channel reconfiguration, CQI report configuration), the eNodeB 1304
instructs the UE 1302 to reconfigure sub-band size to the preferable size. Upon completion the UE 1302
sends a reconfiguration complete message. The signalling proceeds as follows: the eNodeB receives
CQI values from the UE (S1310); these CQI values are used in scheduling by the scheduler 1350
S13 12); downlink transmissions are scheduled by the scheduler in accordance with the CQI values
(S13 16), for which acknowledgements are received (S1318); where the scheduler decides sub-band size
should change (S1314), the sub-band size change is instructed in a size configuration message to the UE
(SI 320); if faster change is needed, MAC header signalling is also applicable; and the eNodeB optionally
receives a reconfiguration complete message from the UE (SI 322).
RRC signalling/application (MTC server) initiated
An alternative technique, suitable for MTC devices having an associated, dedicated, MTC server
1416, is to allow the MTC server 1416 to initiate sub-band size changes at one or more or indeed all
connected MTC devices, A typical procedure entails: sending a configuration message from MTC server
1416 to one or more MTC devices 1402 - step S1410; sending a sub-band size change configuration from
the MTC device(s) 1402 to an eNodeB 1404 - step SI420 - and optionally receiving a "configuration
complete" message from the eNodeB 1404 - step S1430.
There now follows a more detailed description of the main functional components of UEs and
eNodeBs in which embodiments of the invention may suitably be implemented. Throughout the
description, BB refers to Base Band, R refers to Radio Frequency.
Hardware
UE (Terminal) function blocks
As shown in Figure 15, the typical terminal comprises:
an antenna arrangement 1501, which transmits and/or receives the radio signals;
a duplexer 1502, the filter to separate between uplink RF and downlink RF (FDD). In the TDD
case, the duplexer is just an RF switch (switching uplink time slot and downlink time slot);
a Low Noise Amplifier (LNA) 1503, which amplifies the received signal from the antenna 1501;
a down converter 1504, which converts an RF signal to baseband (BB) signal, typically using
quadrature demodulation (I Q output). A variety of receiver architectures, e.g. direct conversion, super
heterodyne etc., may be adopted to provide suitable down-conversion;
a local oscillator (LO) 1505, which re-generates a clock for demodulator, and tracking the
fluctuation of frequency by AFC(Auto Frequency Control) this is also used for modulation clock;
an Analog to Digital converter (A/D) 1506, which converts analog signals to digital signals;
a Digital to Analog converter (D/A) 1507, which converts digital signal to analog signals;
an up converter 1508, which converts BB signal to RF, typically quadrature modulation ( Q BB
input to RF);
a Power amplifier (PA) or High power amplifier 509, which amplifies RF signal from modulator
to the required transmission power;
Baseband circuitry 1510, which provides the baseband processing functions (details are shown
below, see Figure 16);
Protocol circuitry 5 , which performs the processing of Layer2/3/Core Network/TCP related
protocols. Typical protocols in 3GPP are: MAC; RLC; PDCP; RRC; and CN;
Application functions unit 1512, which provides various applications, including speech codec,
web browsing, etc.; and
optional additional units 1513, examples include BPF(Band-pass filter) which may inserted
between the blocks if necessary, depending on architecture or implementation; and/or an IF filter.
UE Baseband function blocks
The terminal baseband 1510, illustrated in Figure 16, comprises the following functional blocks:
CP (Cyclic Prefix) removal unit 1601, which obtains the head of frame timing from
synchronization unit and removes the Cyclic prefix from it;
FFT (Fast Fourier Transform) unit 1602 which converts time domain signal to frequency domain
signal;
an equalizer unit 1603, where the signal which is effected by channel is recovered. Based on the
frequency response of chamiel provided by channel estimation unit, the filter processing is performed;
Channel decoding unit 1604 for performing channel decoding processing such as channel demapping
and de-interleave, error correction etc.;
Synchronization/tracking unit 1605 which performs time and frequency synchronization based on
reference signal, synchronization signal (and frequency tracking, if terminal is moved);
Channel estimation unit 1606; based on reference signals, the channel of radio propagation is
estimated;
Measurement unit 1607 which performs interference/signal strength measurement function
(sometimes RF functions);
S R (Signal to interference and noise ratio) processing unit 1608. Where signal strength is
measured in the reference signals and interference is obtained from measurement unit, the SINR
processing unit calculates the SINR (Signal to Noise + interference ratio) based on these values;
Delay profile calculation unit 1609, in which the channel estimates are aggregated to determine a
delay profile;
PDSCH transmission (Tx) mode selection 1610; wherein, based on eNodeB direction, PDSCH
mode is selected;
Sub-band size selector 1611. Based on one or more of the sub-band size selection methods
described above: i.e. static table look-up, semi-static size selection; SINR, or channel condition (e.g.
delay profile, PDSCH Tx mode, etc. ), a suitable sub-band size is selected. The selected sub-band size is
output as the recommended sub-band size for use in the CQI signalling from the UE;
MCS (Modulation and Coding scheme) selection unit 1612, which selects the preferable MCS
based on current downlink channel quality;
CQI encoding unit 1613;
Channel encoding unit 1614 for encoding the channels into resources, multiplexing the indicators
(e.g. CQI);
FFT (Fast Fourier Transform) unit 1615, which converts time domain signals to frequency
domain signals;
Subcarrier mapping unit 1616, for performing the mapping of the subcarriers to be transmitted
based on scheduler's grant indication;
FFT (Inverse Fast Fourier Transform) 1 17 which converts frequency domain signals to time
domain signals; and
CP (cyclic prefix) addition unit 1618 which inserts cyclic prefix at the head of frame; in
preparation for uplink transmission.
Depending upon implementation other functional blocks may be provided such as S/P (serial to
parallel), P/S (parallel to Serial) conversion function, which would be inserted for OFDM signal
generation/regeneration.
ENodeB (Base station) function blocks
As shown in Figure 17, the typical base station (eNodeB) comprises:
an antenna arrangement 1701, which transmits and receives radio signals. Typically more than
one antenna element is provided for diversity/MFMO transmission;
an RF filter 1702; which separates the RF between uplink RF and downlink RF (FDD) or
frequency bands (e.g. 800MHz, 2.1GHz);
an LNA (Low Noise Amplifier) 1703 which amplifies the received signal from antenna;
RF transceiver 1704 which up converts from BB to RF, and down converts from RF to BB as
required;
Baseband circuitry 1705 which provides the baseband functionality such as channel
coding/decoding, modulation/demodulation, channel estimation, equalization etc. (discussed in more
detail in the description of Figure 1 below);
Scheduler 1706 for scheduling the downlink data/uplink data for a UE based on CQI report and
measurement of internal resources (power, buffer status, interference etc.);
Protocol circuitry 1707 for performing the processing of Layer2/3/Core Network/TCP related
protocols - typical protocols in 3GPP are MAC (Media Access Control), RLC (Radio Link Control),
PDCP ( Packet data compressed protocol), and RRC (Radio Resource control);
External interface 1708; which provides the interface to external nodes such as SI (fromyto Core
Network) and X2 (from/to other eNodeB s);
Location information circuitry 1709, which obtain location information. This is an optional
functionality e.g. GPS global positioning system or another location measurement.
PA (Power amplifier or High power amplifier) 1710 which amplifies RF signals from RF
transceiver to the required transmission power.
Note; these are logical functions. They are sometimes provided in physically separated apparatus.
For example, RRH (Radio remote Header) may split the RF function from main base station and install it
in another location some distance from the main base station.
The antenna arrangement 1701 is usually located on the mast/tower or top of the roof and
connected with feeder.
The baseband 1705, scheduling 1706 and protocol 1707 functions may be installed into one
cabinet, the remaining functions may be installed outside the base station.
eNodeB baseband function blocks
The base station baseband, illustrated in Figure 18, comprises:
CP (Cyclic Prefix) removal unit 1801, which identify the head of frame from synchronization unit
and removes the cyclic prefix from it;
FFT (Fast Fourier transform) unit 1802, which converts time domain signals to frequency domain
signals;
Equalizer unit 1803, where the signal which is effected by channel is recovered (amplitude and
phase);
IFFT (Inverse Fast Fourier transform) unit 1804 which converts frequency domain signals to time
domain signals;
P/S (Parallel to Serial) conversion unit 1811 which provides a conversion function for OFDM
signal generation;
Channel decoding unit 1805, which performs channel decoding like de-mapping and deinterleave,
error correction etc;
CQI decoding unit 1806, which de-multiplexes the control signals and the decoding CQI;
sub-band channel quality unit 1807, which obtains the sub-band channel quality values and
outputs them to the scheduler;
Sub-band scheduling unit 1808, which delivers the output schedule from scheduler;
MCS (Modulation and Coding scheme) selection unit 1809, which selects the MCS based on
current CQI of sub-band;
Channel encoding unit 1810, for encoding the channels into resources, including indicator ( e.g.
CQI);
Subcarrier mapping unit 1812, which maps the subcarriers to be transmitted based on scheduler's
indication of resource allocation;
IFFT (Inverse Fast Fourier Transform) unit 1813 for converting frequency domain signals to time
domain signals;
CP (cyclic prefix) addition unit 1814, which inserts a cyclic prefix at the head of frame in
preparation for downlink transmission;
Synchronization/tracking/timing advance module 1815, which carries out the time and frequency
synchronization based on reference signal, synchronization signal, etc. (and frequency tracking, if
terminal is moved);
Channel estimation module 1816, which based on reference signal, estimates the channel of radio
propagation;
Measurement unit 1817, where interference/signal strength measurement function is performed
(sometimes RF functions)
SINR (Signal to interference ratio) unit 1818, which performs interference measurement function
(sometimes RF functions); and
PDSCH transmission mode selection unit 1819, which selects PDSCH mode based on eNodeB
direction.
Other functional blocks may be provided thus S/P (serial to parallel) conversion function is
inserted for OFDM signal generation.
Network structure
As was briefly discussed in relation to Figure 1, an LTE/SAE network has a number of essential
components. In many MTC applications further functional entities are required. An MTC network
system may comprise:
MTC terminals 102 - UEs which have MTC functions;
eNodeB/eNB 104 - base station for both MTC and non-MTC devices, this is also a function of LTE
(Host carrier);
Serving gateway (S-GW) 112 - for providing user plane function of LTE/SAE, Packet routing and
forwarding, mobility anchoring , this is the gateway between Core network (non-access substratum,
NAS) entities and Radio Access network (RAN)
PDN (Packet Data Network) gateway (P-GW) 114 - for providing user plane function of LTE/SAE
such as UE GR address allocation, packet filtering, EPS bearer configuration. This is the gateway
between core network and Packet Data Network (e.g. external 3GPP networks, other internetworks).
MME (Mobility Management Entity) 106 - for providing control plane function of LTE/SAE such
as NAS signalling, security, Idle mode UE Reachability, PDN GW and Serving G selection.
HSS (Home Subscriber server) 108 - the database of subscribers including information such as user
identifier, key, connected P-GW, the tracking area information (allowing a UE to be located with the
coverage of the network)
MTC (Machine type communication) Server 1 6 - the server of MTC functions
MTC gateway 120 (optional); this represents a gateway between 3GPP/LTE and non LTE MTC
terminals (e.g. LTE to Zigbee interface). The gateway runs M2M Application(s) using M2M Service
Capabilities. The Gateway acts as a proxy between M2M Devices and the Network Domain. The
M2M Gateway may provide service to other devices (e.g. legacy) connected to it that are hidden from
the Network Domain. As an example, an M2M Gateway may run an application that collects and
treats various information (e.g. from sensors and contextual parameters). [ETSI TS.102. 690 VI. 1.1
gives further details of the functionalities of MTC gateways].
Protocol structure
The LTE/SAE/MTC protocol stack is illustrated in Figure 19. The protocol stack comprises:
1. Ll(Layerl) Physical layer processing like modulation/demodulation, channel coding/decoding.
2. MAC(Media Access Control) Hybrid ARQ, scheduling(eNodeB)
3. RLC(Radio Link Control) ARQ Retransmission
4. PDCP(Packet Data Convergence Protocol) packet header reduction/recovery
5. RRC(Radio Resource control) controlling signalling of radio resources.
These are a part of the radio access network (RAN)
6. CN(Core Network); core network functions such as mobility management, tunneling protocol,
session management, bearer management, QoS, security functions
7. MTC application; application for MTC functions
UEs 1902 and other terminals in the network, such as MTC gateways 1920, share the same basic
protocol stack: physical (Ll/PHY), MAC, RLC, PDCP and RRC. The terminals 1902, 1920 share the
core network protocol - typically an Internet Protocol, GR - with the Core Network 1910. A further
protocol layer (referred to as the MTC application layer) is provided to facilitate communication between
MTC devices/gateways 1902/1920 and an MTC server 1916.
MTC features
As mentioned above, the anticipated widespread deployment of third and fourth generation
networks has led to the parallel development of a class of devices and applications which, rather than
taking advantage of the high data rates available, instead take advantage of the robust radio interface and
increasing ubiquity of the coverage area. This parallel class of devices and applications includes MTC
devices and so-called machine to machine (M2M) applications, wherein semi-autonomous or autonomous
wireless communication devices typically communicate small amounts of data on a relatively infrequent
basis.
Examples of MTC (and M2M) devices include: so-called smart meters which, for example, are
located in a customer's house and periodically transmit information back to a central MTC server data
relating to the customers consumption of a utility such as gas, water, electricity and so on; "track and
trace" applications such as transportation and logistics tracking, road tolling and monitoring systems;
remote maintenance and control systems with MTC-enabled sensors, lighting, diagnostics etc.;
environment monitoring; point of sales payment systems and vending machines; security systems, etc.
Further information on characteristics of MTC-type devices and further examples of the
applications to which MTC devices may be applied can be found, for example, in the corresponding
standards, such as ETSI TS 122 368 V10.530 (201 1-07) / 3GPP TS 22.368 version 10.5.0 Release 10) [I].
Whilst it can be convenient for a terminal such as an MTC type terminal to take advantage of the
wide coverage area provided by a third or fourth generation mobile telecommunication network, there are
at present disadvantages and challenges to successful deployment. Unlike a conventional third or fourth
generation terminal device such as a smartphone, an MTC-type terminal is preferably relatively simple
and inexpensive: in addition MTC-devices are often deployed in situations that do not afford easy access
for direct maintenance or replacement - reliable and efficient operation can be crucial. Furthermore,
while the type of functions performed by the MTC-type terminal (e.g. collecting and reporting back data)
do not require particularly complex processing to perform, third and fourth generation mobile
telecommunication networks typically employ advanced data modulation techniques (such as 16QAM or
64QAM) on the radio interface which can require more complex and expensive radio transceivers to
implement.
A "virtual carrier" tailored to low capability terminals such as MTC devices is thus provided
within the transmission resources of a conventional OFDM type downlink carrier (i.e. a "host carrier").
Unlike data transmitted on a conventional OFDM type downlink carrier, data transmitted on the virtual
carrier can be received and decoded without needing to process the full bandwidth of the downlink host
OFDM carrier, for at least some part of a subframe. Accordingly, data transmitted on the virtual carrier
can be received and decoded using a reduced complexity receiver unit.
The term "virtual carrier" corresponds in essence to a narrowband carrier for MTC-type devices
within a host carrier for an OFDM-based radio access technology (such as WiMAX or LTE).
The virtual carrier concept is described in a number of co-pending patent applications (including
GB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB
1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6 [9]), the contents of which are incorporated herein
by reference. For ease of reference, however, an overview of certain aspects of the concept of virtual
carriers is set out in Annex 1.
Other narrowband scenarios
While the preceding discussion of narrowband system bandwidths (i.e. system bandwidths below
6RBs in frequency where conventional systems do not provide sub-band CQI reports) have related to
"virtual carrier" systems, especially when considering the "6 Bs" case, the reader will readily appreciate
that the same considerations apply equally to other cases where the system bandwidth is limited, for
instance to 5MHz.
ANNEX 1
The virtual carrier concept is described in a number of co-pending UK patent applications
(including GB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8
[6], GB 1101982.5 [7], GB 101980.9 [8] and GB 1101972.6 [9]). Certain aspects of the concept of
virtual carriers are set out below. In this section, the following abbreviations are frequently adopted:
virtual carrier - VC, host carrier - HC, user equipment - UE, resource block - RB, radio frequency - RF,
and baseband BB.
Like conventional OFDM, the virtual carrier concept has a plurality of subcarriers disposed at
predetermined offsets from a central frequency: the central frequency thus characterises the entire virtual
carrier.
Typical virtual carrier bandwidth is six resource blocks, (i.e. 72 subcarriers) which is in line with
minimum 3GPP bandwidth in LTE. However, as will be seen in the following description, the bandwidth
of VC is by no means restricted to 6RBs.
In line with Release 8 of the 3GPP standard for LTE (REL8 LTE), VC resources are typically
located in the resource blocks centred on the host carrier centre frequency and symmetrically allocated (at
either side of that HC centre frequency) regardless of system bandwidth.
Figure 20 is a schematic diagram of a grid which illustrates the structure of a downlink LTE
subframe with a virtual carrier subsystem 2006 occupying the resource blocks centred on the host carrier
centre frequency 2002. The virtual carrier central frequency, (f2+fl)/2, is selected to be the central
frequency, fc, of the host carrier.
The first n symbols form the control region 2000 which is reserved for the transmission of
downlink control data such as data transmitted on the PDCCH, PCFICH or PHICH.
The signals on the virtual carrier 2006 are arranged such that signals transmitted by the host
carrier that a terminal device operating on the host carrier would require for correct operation and expect
to find in a known pre-determined location are maintained.
Before a conventional LTE terminal can begin transmitting and receiving data in a cell, it first
camps on to the cell. Similarly, an adapted camp-on process can be provided for terminals using the
virtual carrier. A suitable camp-on process for virtual carriers is described in detail in GB 1113801.3
[10]: this camp-on process is incorporated herein by reference.
In the T-shaped operation of Figure 20, the virtual carrier location information, if provided, can
be provided elsewhere in the host carrier. In other implementations of virtual carriers it may be
advantageous to provide this information in the centre band, for example because a virtual carrier
terminal may configure its receiver to operate in a narrow band about the centre band and the virtual
carrier terminal then does not need to adjust its receiver settings for finding the location information.
Depending on the amount of virtual carrier location information provided, the virtual carrier
terminal can either adjust its receiver to receive the virtual carrier transmissions, or it may require further
location information before it can do so.
If for example, the virtual carrier terminal was provided with location information indicating a
virtual carrier presence and/or a virtual carrier bandwidth but not indicating any details as to the exact
virtual carrier frequency range, or if the virtual carrier terminal was not provided with any location
information, the virtual carrier terminal could then scan the host carrier for a virtual carrier (e.g.
performing a so-called blind search process). This process too is discussed in detail in GB 1113801.3
[10].
The following numbered clauses provide further example aspects and features of the present
technique:
1. A method for reporting channel state information corresponding to a communication link
between a terminal device and a base station in a wireless communications system, the wireless
communication system having a system bandwidth divided into a plurality of sub-band parts having at
least one characteristic sub-band size, the method comprising:
providing a plurality of communications resource elements across the system bandwidth;
measuring one or more channel state parameter corresponding to the channel state in one or more
of the communications resource elements;
generating aggregate channel state information from at least one measured channel state
parameter corresponding to the channel state of the communications resource elements,
generating sub-band channel state information from at least one measured channel state parameter
corresponding to the channel state of the communications resource elements within respective sub-band
parts,
wherein the size of the sub-band part is dependent upon radio propagation conditions.
2. A method according to clause 1, the wireless communication system further having a
subsystem bandwidth divided into a plurality of subsystem sub-band parts, the method further
comprising:
providing a plurality of subsystem communications resource elements across the subsystem
bandwidth;
generating subsystem channel state information from at least one measured channel state
parameter corresponding to the channel state of the subsystem communications resource elements,
generating subsystem sub-band channel state information from at least one measured channel
state parameter corresponding to the channel state of the communications resource elements within
respective subsystem sub-band parts,
wherein the size of the subsystem sub-band part is dependent upon radio propagation conditions.
3. A method according to clause 1 or 2, wherein the size of the sub-band part is broadcast in
radio resource signalling.
4. A method according to clause 1 or 2, wherein the method further comprises:
determining at least one category of radio propagation condition associated with the
communication link;
providing a lookup table listing sub-band sizes corresponding to category of radio propagation
conditions; and
selecting the sub-band size associated with the determined category.
5. A method according to clause 4, wherein the categorised radio propagation conditions
include at least one radio propagation condition selected from a group of radio propagation conditions
including:
a site type of the base station;
a morphology type of the base station location;
a mobility type of the terminal device; and
an indicator of the type of base station.
6. A method according to any preceding clause, wherein the method further comprises:
determining at least one category of ambient radio propagation condition;
calculating a sub-band size in accordance with at least one ambient radio propagation condition;
and
selecting the sub-band size associated with the determined category.
7 . A method according to clause 8, wherein the categorised ambient radio propagation
condition include at least one radio propagation condition selected from a group of ambient radio
propagation conditions including:
a measure of delay spread;
a SIN measurement; and
an indicator of the transmission mode of a downlink data channel.
8. A method according to any of clauses 1to 5, wherein the method further comprises:
measuring at least one radio propagation characteristic experienced by a UE;
calculating a dynamic sub-band size in accordance with the measured radio propagation
characteristic; and
using the dynamic sub-band size as the sub-band size for a predetermined period of time.
9. A method according to clause 8, wherein the measured radio propagation characteristic
includes at least one radio propagation characteristic selected from a group of measured parameters
including:
a measure of delay spread;
a SINR measurement; and
an indicator of the transmission mode of a downlink data channel.
10. A method according to any preceding clause, further comprising signalling a change of
size of the sub-band part, wherein the change of sub-band size corresponding to a change in radio
propagation conditions is indicated in LI signalling.
11. A method according to any of clauses 1 to 9, further comprising signalling a change of
size of the sub-band part, wherein the change of sub-band size corresponding to a change in radio
propagation conditions is indicated in radio resource signalling.
12. A method according to any preceding clause, wherein the plurality of sub-band parts
have a plurality of characteristic sub-band sizes, at least a first group of the sub-band parts having a first
characteristic sub-band size and a second group of the sub-band parts having a second characteristic subband
size, the first characteristic sub-band size and second characteristic sub-band size being different,
thereby facilitating reporting channel state information at different degrees of granularity for different
parts of the system bandwidth.
13. A terminal device for reporting channel state information corresponding to a
communication link to a base station in a wireless communications system, the wireless communication
system having an system bandwidth divided into a plurality of sub-band parts having at least one
characteristic sub-band size and providing a plurality of communications resource elements across the
system bandwidth, the terminal device comprising:
a measurement unit operable to measure one or more channel state parameter corresponding to
the channel state in one or more of the communications resource elements; and
a processing unit operable to generate aggregate channel state information from at least one
measured channel state parameter corresponding to the channel state of the communications resource
elements, and to generate sub-band channel state information from at least one measured channel state
parameter corresponding to the channel state of the communications resource elements within respective
sub-band parts,
wherein the size of the sub-band part is dependent upon radio propagation conditions.
14. A terminal device according to clause 13, the wireless communication system further
having a subsystem bandwidth divided into a plurality of subsystem sub-band parts and providing a
plurality of subsystem communications resource elements across the subsystem bandwidth,
wherein the processing unit is further operable to generate subsystem channel state information
from at least one measured channel state parameter corresponding to the channel state of the subsystem
communications resource elements, and
to generate subsystem sub-band channel state information from at least one measured channel
state parameter corresponding to the channel state of the communications resource elements within
respective subsystem sub-band parts,
wherein the size of the subsystem sub-band part is dependent upon radio propagation conditions.
15. A terminal device according to clause 13 or 14, further comprising protocol circuitry
adapted to prepare uplink signals conforming to the radio resource control, RRC, protocol, wherein the
size of the sub-band part is broadcast in radio resource signalling.
16. A terminal device according to clause 13 or 14, the terminal device further comprising a
sub-band size selector adapted to determine at least one category of radio propagation condition
associated with the communication link; the sub-band size selector including a database storing a lookup
table listing sub-band sizes corresponding to category of radio propagation conditions; wherein the subband
size selector defines the sub-band size to be the sub-band size associated with the determined
category.
17. A terminal device according to clause 16, wherein the categorised radio propagation
conditions include at least one radio propagation condition selected from a group of radio propagation
conditions including:
a site type of the base station;
a morphology type of the base station location;
a mobility type of the terminal device; and
an indicator of the type of base station .
18. A terminal device according to clause 13 or 14, the terminal device further comprising a
sub-band size selector adapted to determine at least one category of ambient radio propagation condition,
the sub-band size selector calculating a sub-band size in accordance with the determined category of at
least one ambient radio propagation condition; wherein the sub-band size selector defines the sub-band
size to be the sub-band size associated with the determined category.
19. A terminal device according to clause 18, wherein the categorised ambient radio
propagation condition includes at least one radio propagation condition selected from a group of ambient
radio propagation conditions including:
a measure of delay spread;
a SINK measurement; and
an indicator of the transmission mode of a downlink data channel.
20. A tenninal device according to clause 13 or 14, wherein the measurement unit is further
operable to measure at least one radio propagation characteristic experienced by the terminal device; and
the terminal device further comprising a sub-band size selector adapted to calculate a dynamic sub-band
size in accordance with the measured radio propagation characteristic and to use the dynamic sub-band
size as the sub-band size for a predetermined period of time.
21. A terminal device according to clause 20, wherein the measured radio propagation
characteristic includes at least one radio propagation characteristic selected from a group of measured
parameters including:
a measure of delay spread;
a SI R measurement; and
an indicator of the transmission mode of a downlink data channel.
22. A terminal device according to any of clauses 13 to 21, further comprising means for
signalling a change of size of the sub-band part and protocol circuitry adapted to prepare uplink signals
conforming to a layer 1, LI, protocol, wherein the change of sub-band size corresponding to a change in
radio propagation conditions is indicated in LI signalling.
23. A terminal device according to any of clauses 13 to 21, further comprising means for
signalling a change of size of the sub-band part and protocol circuitry adapted to prepare uplink signals
conforming to the radio resource control, RRC, protocol, wherein the change of sub-band size
corresponding to a change in radio propagation conditions is indicated in radio resource signalling.
24. A terminal device according to any of clauses 13 to 23, wherein the plurality of sub-band
parts have a plurality of characteristic sub-band sizes, at least a first group of the sub-band parts having a
first characteristic sub-band size and a second group of the sub-band parts having a second characteristic
sub-band size, the first characteristic sub-band size and second characteristic sub-band size being
different, thereby facilitating reporting channel state information at different degrees of granularity for
different parts of the system bandwidth.
REFERENCES
[1] ETSI TS 122 368 V10.530 (2011-07) / 3GPP TS 22.368 version 10.5.0 Release 10)
[2] UK patent application GB 1101970.0
[3] UK patent application GB 110198 .7
[4] UK patent application GB 1101966.8
[5] UK patent application GB 101983 .3
[6] UK patent application GB 1101853.8
[7] UK patent application GB 1101982.5
[8] UK patent application GB 1101980.9
[9] UK patent application GB 1101972.6
[10] UK patent application GB 1113801 .3
[11] UK patent application GB 1121767.6
P101430PCT 30

CLAIMS
1. A method for reporting channel state information corresponding to a communication link
between a terminal device and a base station in a wireless communications system, the wireless
communication system having a system bandwidth divided into a plurality of sub-band parts having at
least one characteristic sub-band size, the method comprising:
providing a plurality of communications resource elements across the system bandwidth;
measuring one or more channel state parameter corresponding to the channel state in one or more
of the communications resource elements;
generating aggregate channel state information from at least one measured channel state
parameter corresponding to the channel state of the communications resource elements,
generating sub-band channel state information from at least one measured channel state parameter
corresponding to the channel state of the communications resource elements within respective sub-band
parts,
wherein the size of the sub-band part is dependent upon radio propagation conditions.
2. A method as claimed in Claim 1, the wireless communication system further having a
subsystem bandwidth divided into a plurality of subsystem sub-band parts, the method further
comprising:
providing a plurality of subsystem communications resource elements across the subsystem
bandwidth;
generating subsystem channel state information from at least one measured channel state
parameter corresponding to the channel state of the subsystem communications resource elements,
generating subsystem sub-band channel state information from at least one measured channel
state parameter corresponding to the channel state of the communications resource elements within
respective subsystem sub-band parts,
wherein the size of the subsystem sub-band part is dependent upon radio propagation conditions.
3. A method as claimed in Claim 1 or Claim 2, wherein the size of the sub-band part is
broadcast in radio resource signalling.
4. A method as claimed in Claim 1 or Claim 2, wherein the method further comprises:
determining at least one category of radio propagation condition associated with the
communication link;
providing a lookup table listing sub-band sizes corresponding to category of radio propagation
conditions; and
selecting the sub-band size associated with the determined category.
P101430PCT 3 1
5. A method as claimed in Claim 4, wherein the categorised radio propagation conditions
include at least one radio propagation condition selected from a group of radio propagation conditions
including:
a site type of the base station;
a morphology type of the base station location;
a mobility type of the terminal device; and
an indicator of the type of base station.
6. A method as claimed in any one of the preceding Claims, wherein the method further
comprises:
determining at least one category of ambient radio propagation condition;
calculating a sub-band size in accordance with at least one ambient radio propagation condition;
and
selecting the sub-band size associated with the determined category.
7. A method as claimed in Claim 8, wherein the categorised ambient radio propagation
condition include at least one radio propagation condition selected from a group of ambient radio
propagation conditions including:
a measure of delay spread;
a SINR measurement; and
an indicator of the transmission mode of a downlink data channel.
8. A method as claimed in any one of Claims 1 to 5, wherein the method further comprises:
measuring at least one radio propagation characteristic experienced by a UE;
calculating a dynamic sub-band size in accordance with the measured radio propagation
characteristic; and
using the dynamic sub-band size as the sub-band size for a predetermined period of time.
9. A method as claimed in Claim 8, wherein the measured radio propagation characteristic
includes at least one radio propagation characteristic selected from a group of measured parameters
including:
a measure of delay spread;
a SINR measurement; and
an indicator of the transmission mode of a downlink data channel.
10. A method as claimed in any one of the preceding Claims, further comprising signalling a
change of size of the sub-band part, wherein the change of sub-band size corresponding to a change in
radio propagation conditions is indicated in LI signalling.
P101430PCT 32
11. A method as claimed in any one of Claims 1 to 9, further comprising signalling a change
of size of the sub-band part, wherein the change of sub-band size corresponding to a change in radio
propagation conditions is indicated in radio resource signalling.
12. A method as claimed in any one of the preceding Claims, wherein the plurality of subband
parts have a plurality of characteristic sub-band sizes, at least a first group of the sub-band parts
having a first characteristic sub-band size and a second group of the sub-band parts having a second
characteristic sub-band size, the first characteristic sub-band size and second characteristic sub-band size
being different, thereby facilitating reporting channel state information at different degrees of granularity
for different parts of the system bandwidth.
13. A terminal device for reporting channel state information corresponding to a
communication link to a base station in a wireless communications system, the wireless communication
system having an system bandwidth divided into a plurality of sub-band parts having at least one
characteristic sub-band size and providing a plurality of communications resource elements across the
system bandwidth, the terminal device comprising:
a measurement unit operable to measure one or more channel state parameter corresponding to
the channel state in one or more of the communications resource elements; and
a processing unit operable to generate aggregate channel state information from at least one
measured channel state parameter corresponding to the channel state of the communications resource
elements, and to generate sub-band channel state information from at least one measured channel state
parameter corresponding to the channel state of the communications resource elements within respective
sub-band parts,
wherein the size of the sub-band part is dependent upon radio propagation conditions.
14. A terminal device as claimed in Claim 13, the wireless communication system further
having a subsystem bandwidth divided into a plurality of subsystem sub-band parts and providing a
plurality of subsystem communications resource elements across the subsystem bandwidth,
wherein the processing unit is further operable to generate subsystem channel state information
from at least one measured channel state parameter corresponding to the channel state of the subsystem
communications resource elements, and
to generate subsystem sub-band channel state information from at least one measured channel
state parameter corresponding to the channel state of the communications resource elements within
respective subsystem sub-band parts,
wherein the size of the subsystem sub-band part is dependent upon radio propagation conditions.
15. A terminal device as claimed in Claim 13 or Claim 14, further comprising protocol
circuitry adapted to prepare uplink signals conforming to the radio resource control, RRC, protocol,
wherein the size of the sub-band part is broadcast in radio resource signalling.
P101430PCT 33
16. A terminal device as claimed in Claim 13 or Claim 14, the terminal device further
comprising a sub-band size selector adapted to determine at least one category of radio propagation
condition associated with the communication link; the sub-band size selector including a database storing
a lookup table listing sub-band sizes corresponding to category of radio propagation conditions; wherein
the sub-band size selector defines the sub-band size to be the sub-band size associated with the
determined category.
17. A terminal device as claimed in Claim 16, wherein the categorised radio propagation
conditions include at least one radio propagation condition selected from a group of radio propagation
conditions including:
a site type of the base station;
a morphology type of the base station location;
a mobility type of the terminal device; and
an indicator of the type of base station.
18. A terminal device as claimed in Claim 13 or Claim 14, the terminal device further
comprising a sub-band size selector adapted to determine at least one category of ambient radio
propagation condition, the sub-band size selector calculating a sub-band size in accordance with the
determined category of at least one ambient radio propagation condition; wherein the sub-band size
selector defines the sub-band size to be the sub-band size associated with the determined category.
19. A terminal device as claimed in Claim 18, wherein the categorised ambient radio
propagation condition includes at least one radio propagation condition selected from a group of ambient
radio propagation conditions including:
a measure of delay spread;
a S measurement; and
an indicator of the transmission mode of a downlink data channel.
20. A tenninal device as claimed in Claim 13 or Claim 14, wherein the measurement unit is
further operable to measure at least one radio propagation characteristic experienced by the terminal
device; and the terminal device further comprising a sub-band size selector adapted to calculate a
dynamic sub-band size in accordance with the measured radio propagation characteristic and to use the
dynamic sub-band size as the sub-band size for a predetermined period of time.
21. A terminal device as claimed in Claim 20, wherein the measured radio propagation
characteristic includes at least one radio propagation characteristic selected from a group of measured
parameters including:
a measure of delay spread;
a SINR measurement; and
an indicator of the transmission mode of a downlink data channel.
P101430PCT 34
22. A terminal device as claimed in any one of Claims 3 to 21, further comprising means for
signalling a change of size of the sub-band part and protocol circuitry adapted to prepare uplink signals
conforming to a layer 1, LI, protocol, wherein the change of sub-band size corresponding to a change in
radio propagation conditions is indicated in L signalling.
23. A terminal device as claimed in any one of Claims 13 to 21, further comprising means for
signalling a change of size of the sub-band part and protocol circuitry adapted to prepare uplink signals
conforming to the radio resource control, RRC, protocol, wherein the change of sub-band size
corresponding to a change in radio propagation conditions is indicated in radio resource signalling.
24. A terminal device as claimed in any one of Claims 13 to 23, wherein the plurality of subband
parts have a plurality of characteristic sub-band sizes, at least a first group of the sub-band parts
having a first characteristic sub-band size and a second group of the sub-band parts having a second
characteristic sub-band size, the first characteristic sub-band size and second characteristic sub-band size
being different, thereby facilitating reporting channel state information at different degrees of granularity
for different parts of the system bandwidth.