COMMUNICATING RF TERMINAL CAPABILITY
BACKGROUND OF THE INVENTION
The present invention relates to methods, systems and apparatus for allocating transmission
resources and transmitting data in mobile telecommunication systems.
Embodiments of the present invention can for example allocate of transmission resources to
machine type communication (MTC) devices in cellular telecommunications networks having
orthogonal frequency division multiplex (OFDM) based radio access technology (such as WiMAX
and LTE).
Certain classes of telecommunications device, such as MTC devices (e.g. semi-autonomous or
autonomous wireless communication terminals), support "low capability" communication applications
that are characterised, for instance, by the transmission of small amounts of data at relatively
infrequent intervals.
In many scenarios, it is preferable to provide terminals dedicated to such "low capability"
communication applications with a simple receiver unit (or transceiver unit) having capabilities more
commensurate with the amount of data likely to be transmitted to (or from) the terminal. This more
limited capability contrasts with the capabilities of the conventional mobile telecommunications
terminals, such as smartphones, which share access to the same telecommunications networks.
To support MTC terminals, it has been proposed to introduce a "virtual carrier" operating
within a bandwidth of one or more "host carriers": the proposed virtual carrier concept preferably
integrates within the transmission resources of conventional OFDM based radio access technologies
and subdivides frequency spectrum in a similar manner to OFDM. 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 OFDM host carrier.
Accordingly, data transmitted on the virtual carrier can be received and decoded using a reduced
complexity receiver unit: with concomitant benefits such as increased simplicity, increased reliability,
reduced form-factor and lower manufacturing cost.
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.
In one version of the virtual carrier concept a plurality of subcarriers are disposed at
predetermined offsets from a central frequency, similar to the subcarrier structure in conventional
OFDM: the central frequency may be viewed as characterising the whole virtual carrier. The virtual
carrier central frequency is typically selected to be the central frequency of the host carrier.
Direct conversion receiver architectures are attractive for manufacturers of mass market
communication devices, such as MTC devices, because of their simplicity and lower cost. The
communications networks have therefore adapted their standards to permit the adoption of such
architectures. One adaptation has been to stipulate that the standard should not use a frequency band
where direct conversion receivers are likely to encounter disruptive levels of interference arising from
imperfections in the receiver itself (i.e. self-mixing) - the unused frequency band is commonly
referred to as the DC subcarrier, where DC stands for "direct current": non-use of a frequency band is
typically achieved by not transmitting a carrier wave at the frequency band in downlink transmissions
from a base station in the communications networks.
An efficient operation of a wireless telecommunications system for MTC devices is therefore
desirable.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a terminal having: a radiofrequency,
RF, receiving portion for receiving RF signals from a base station, the RF receiving portion
having an associated bandwidth status, said bandwidth status defining to which mode of virtual
channel operation the terminal device is to be assigned; a capability reporting unit adapted to
determine the bandwidth status of the RF receiving portion of the terminal device; and an RF
transmitting portion for communicating control data to the base station, wherein the control data
includes the bandwidth status.
The terminal and base station preferably communicate data in a wireless telecommunications
system using a first plurality of Orthogonal Frequency Division Multiplex, OFDM, sub-carriers
spanning a first frequency bandwidth, at least one of said subcarriers being an unused centre frequency
for the first frequency bandwidth, and wherein the mode of virtual channel operation relates to a
virtual channel, the virtual channel being a group of sub-carriers selected from said first plurality of
OFDM sub-carriers and spanning a second frequency bandwidth, said second frequency bandwidth
being substantially narrower than the first frequency bandwidth.
The terminal may have a first bandwidth status, first bandwidth status representing an
indication that the terminal has a receiver that can receive radio frequency, RF, signals over the first
frequency bandwidth and baseband signals over a second frequency bandwidth, The first bandwidth
status may correspond to a baseband narrow band type of receiver architecture as described hereafter.
Alternatively or additionally, the terminal may have a second bandwidth status, second
bandwidth status representing an indication that the terminal has a receiver that can receive radio
frequency, RF, signals and baseband signals over the second frequency bandwidth. The second
bandwidth status may correspond to a normal narrow band type of receiver architecture as described
hereafter.
Conveniently, the base station may include a capacity monitoring unit for determining the
level of data traffic on virtual channels, and in the case where both the level of data traffic in the
virtual channel is determined to exceed a capacity threshold level and the terminal is determined to
have a second bandwidth status, second bandwidth status representing an indication that the terminal
has a receiver that can receive radio frequency, RF, signals and baseband signals over the second
frequency bandwidth: the centre frequency for the virtual channel is assigned to a frequency
substantially distinct from the centre frequency for the first frequency bandwidth, the base station is
further configured to designate the assigned centre frequency as an unused centre frequency for the
virtual channel; and the at least one unused subcarrier allocated to the assigned centre frequency is the
designated unused centre frequency.
Preferably, the bandwidth status represents an indication of a classification of receiver
architecture selected from a group including: intermediate frequency conversion, direct conversion,
normal narrowband and baseband narrowband.
Alternatively or in addition, the bandwidth status may correspond to at least one parameter
characterising the bandwidth size capability of the receiver. The bandwidth size capability may relate
to the radio frequency capability and/or the baseband capability of the receiver.
It has been seen as desirable to extend the concept of virtual carriers to blocks of OFDM
subcarriers that are not centred on the host carrier central frequency. Co-pending patent application
number GB 1113801.3 [ 1 1] describes one arrangement where there is a plurality of MTC devices and
the central frequency of at least some of the virtual carriers is not same as the central frequency of the
host carrier.
In this case, there is the risk that the central frequency assigned to the virtual carrier may not
be free of data - and thus that MTC devices with direct conversion receiver architectures may
encounter unwanted interference and consequently that they may operate less effectively in the virtual
carrier.
The communication of control data including the bandwidth status allows base stations to
allocate an unused subcarrier (i.e. a DC subcarrier) efficiently to each terminal device using one or
more resource blocks in virtual carrier mode (such as MTC devices) in accordance with the bandwidth
capability of that terminal device. Depending upon the MTC device capabilities (i.e. bandwidth
status) the central frequency of the virtual carriers need not be the same as the central frequency of the
host carrier yet all MTC devices that might be affected by self-mixing may be assigned virtual carriers
that have suitable "unused" central frequencies.
Whereas known virtual carrier arrangements does not take DC offset impact for direct
conversion receivers into account when the virtual carrier central frequency is different from the host
carrier central frequency, the solution described herein provides a set of solutions for DC subcarrier
allocation for virtual carrier (especially in low cost MTC-type terminals) where a virtual carrier is
allocated in groups of sub-carriers (i.e. resource blocks) other than those centred on the (LTE) host
carrier centre frequency.
Various further aspects and embodiments of the invention are provided in the appended
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 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.
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 provides a schematic diagram illustrating an example of a conventional mobile
telecommunication network;
Figure 2 provides a schematic diagram illustrating a conventional LTE radio frame;
Figure 3A provides a schematic diagram illustrating an example of a conventional LTE
downlink radio sub-frame;
Figure 3B illustrates the position of the DC subcarrier within a band centred upon a host
carrier central frequency in conventional LTE;
Figure 3C shows the finer structure within resource blocks of conventional LTE;
Figure 4 provides a schematic diagram illustrating an example of a LTE downlink radio subframe
in which a virtual carrier has been inserted at the centre frequency of the host carrier;
Figure 5 provides a schematic diagram illustrating an example of a LTE downlink radio subframe
in which virtual carriers have been inserted at a number of frequencies of the host carrier,
requiring allocation of additional unused subcarriers (DC subcarriers) at the centre frequency for each
such virtual carrier;
Figure 6A provides a schematic illustration of a direct conversion (zero-IF) receiver
architecture;
Figure 6B provides a schematic illustration of DC offset arising in a direct conversion (zero
intermediate frequency - zero IF) architecture;
Figure 7 provides a schematic illustration of an "indirect" conversion (e.g. heterodyne)
architecture using an intermediate frequency filter to bypass DC offset;
Figure 8A provides a schematic illustration of the operation of a base station RRM in
determining to which virtual channel to allocate a UE;
Figure 8B provides a schematic illustration of the operation of a base station scheduling unit in
transmitting data to a UE to which a given virtual channel has been assigned;
Figure 8C provides a schematic illustration of the operation of the UE of Figures 8A and 8B;
Figure 9 provides a schematic diagram illustrating two terminal radio frequency architectures:
"normal narrow band" (A) and "baseband narrow band" (B);
Figure 10 provides a schematic diagram of a selection of options in terminal radio frequency
architectures for uplink and downlink the baseband narrow band architecture is further subdivided;
Figure 1 1 provides a schematic diagram illustrating an LTE downlink radio sub-frame in
which a virtual carrier has been inserted in accordance with an embodiment of the invention;
Figure 12A provides a schematic illustration of the operation of a base station RRM in
determining to which virtual channel to allocate a UE, where allocation of virtual carriers depends
upon terminal RF capability, in accordance with an embodiment of the invention;
Figure 12B provides a schematic illustration of the operation of the UE of Figure 12A in
accordance with an example of the present invention;
Figure 12C provides a schematic illustration of the detection of the RF capability of the UE in
Figures 12A and 12B;
Figure 13A provides a schematic illustration of the conventional procedure for UE capability
transfer in e-UTRAN;
Figure 13B illustrates a conventional UE-EUTRA-Capability IE to which new IEs relevant to
MTC-type devices may be appended;
Figure 14 provides a schematic diagram illustrating a part of an LTE cellular
telecommunications network adapted to provide radio access to conventional LTE terminal and
reduced capacity terminals in accordance with an embodiment of the present invention; and
Figure 15 illustrates the distinction between unscheduling and puncturing when leaving a
subcarrier unused.
DETAILED DESCRIPTION
Third and fourth generation mobile telecommunication systems, such as those based on the
3GPP defined UMTS and Long Term Evolution (LTE) architecture are able to support more
sophisticated services than simple voice and messaging services offered by previous generations of
mobile telecommunication systems.
For example, with the improved radio interface and enhanced data rates provided by LTE
systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile
video conferencing that would previously only have been available via a fixed line data connection.
The demand to deploy third and fourth generation networks is therefore strong and the coverage area
of these networks, i.e. geographic locations where access to the networks is possible, is expected to
increase rapidly.
Figure 1 provides a schematic diagram illustrating some basic functionality of a conventional
mobile telecommunications network.
The network includes a plurality of base stations 101 connected to a core network 102. Each
base station provides a coverage area 103 (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) 104. Data is
transmitted from base stations 101 to terminal devices 104 within their respective coverage areas 103
via a radio downlink. Data is transmitted from terminal devices 104 to the base stations 101 via a radio
uplink. The core network 102 routes data to and from the terminal devices 104 via the respective base
stations 101 and provides functions such as authentication, mobility management, charging and so on.
Mobile telecommunications systems such as those arranged in accordance with the 3GPP
defined Long Term Evolution (LTE) architecture use an orthogonal frequency division multiplex
(OFDM) based interface for the radio downlink (so-called OFDMA) and the radio uplink (so-called
SC-FDMA).
Figure 2 shows a schematic diagram illustrating an OFDM based LTE downlink radio frame
201. The LTE downlink radio frame is transmitted from an LTE base station (known as an enhanced
Node B) and lasts 10 ms. The downlink radio frame comprises ten sub-frames, each sub-frame lasting
1 ms. A primary synchronisation signal (PSS) and a secondary synchronisation signal (SSS) are
transmitted in the first and sixth sub-frames of the LTE frame. A primary broadcast channel (PBCH) is
transmitted in the first sub-frame of the LTE frame. The PSS, SSS and PBCH are discussed in more
detail below.
Figure 3A is a schematic diagram of a grid which illustrates the structure of an example
conventional downlink LTE sub-frame. The sub-frame comprises a predetermined number of
"symbols", which are each transmitted over a respective 1ms period. Each symbol comprises a
predetermined number of orthogonal sub-carriers distributed across the bandwidth of the downlink
radio carrier. Here, the horizontal axis represents time while the vertical represents frequency.
As noted above, LTE provides an unused subcarrier 305 at the central frequency of OFDM
host carrier. Figure 3B illustrates the position of the unused subcarrier 305 within a band 310 centred
upon a host carrier central frequency.
The example sub-frame shown in Figure 3A comprises 14 symbols and 1200 sub-carriers
spread across a 20MHz bandwidth, R 2o. The smallest allocation of user data for transmission in LTE
is a "resource block" comprising twelve sub-carriers transmitted over one slot (0.5 sub-frame).
Figure 3C shows the finer structure within each resource block, RB: a resource block
represents a 180kHz band while each subcarrier is spaced 15kHz apart from its neighbours. Each
individual box in the sub-frame grid in Figure 3A corresponds to twelve sub-carriers transmitted on
one symbol.
Figure 3A shows in hatching resource allocations for four LTE terminals 340, 341, 342, 343.
For example, the resource allocation 342 for a first LTE terminal (UE 1) extends over five blocks of
twelve sub-carriers (i.e. 60 sub-carriers), the resource allocation 343 for a second LTE terminal (UE2)
extends over six blocks of twelve sub-carriers and so on.
Control channel data is transmitted in a control region 300 (indicated by dotted-shading in
Figure 3) of the sub-frame comprising the first n symbols of the sub-frame where n can vary between
one and three symbols for channel bandwidths of 3MHz or greater and where n can vary between two
and four symbols for channel bandwidths of 1.4MHz. For the sake of providing a concrete example,
the following description relates to host carriers with a channel bandwidth of 3MHz or greater so the
maximum value of n will be 3 . The data transmitted in the control region 300 includes data transmitted
on the physical downlink control channel (PDCCH), the physical control format indicator channel
(PCFICH) and the physical HARQ indicator channel (PHICH).
PDCCH contains control data indicating which sub-carriers on which symbols of the subframe
have been allocated to specific LTE terminals. Thus, the PDCCH data transmitted in the control
region 300 of the sub-frame shown in Figure 3 would indicate that UE1 has been allocated the block
of resources identified by reference numeral 342, that UE2 has been allocated the block of resources
identified by reference numeral 343, and so on.
PCFICH contains control data indicating the size of the control region (i.e. between one and
three symbols).
PHICH contains HARQ (Hybrid Automatic Request) data indicating whether or not
previously transmitted uplink data has been successfully received by the network.
Symbols in the central band 310 of the time-frequency resource grid are used for the
transmission of information including the primary synchronisation signal (PSS), the secondary
synchronisation signal (SSS) and the physical broadcast channel (PBCH). This central band 310 is
typically 72 sub-carriers wide (corresponding to a transmission bandwidth of 1.08 MHz). The PSS and
SSS are synchronisation signals that once detected allow an LTE terminal device to achieve frame
synchronisation and determine the cell identity of the enhanced Node B transmitting the downlink
signal. The PBCH carries information about the cell, comprising a master information block (MIB)
that includes parameters that LTE terminals use to properly access the cell. Data transmitted to
individual LTE terminals on the physical downlink shared channel (PDSCH) can be transmitted in
other resource elements of the sub-frame. Further explanation of these channels is provided below.
Figure 3A also shows a region of PDSCH 344 containing system information and extending
over a bandwidth of R344 . A conventional LTE frame will also include reference signals which are
discussed further below but not shown in Figure 3A in the interests of clarity.
The number of sub-carriers in an LTE channel can vary depending on the configuration of the
transmission network. Typically this variation is from 72 sub carriers contained within a 1.4MHz
channel bandwidth to 1200 sub-carriers contained within a 20MHz channel bandwidth (as
schematically shown in Figure 3A). As is known in the art, data transmitted on the PDCCH, PCFICH
and PHICH is typically distributed on the sub-carriers across the entire bandwidth of the sub-frame to
provide for frequency diversity. Therefore a conventional LTE terminal must be able to receive the
entire channel bandwidth in order to receive and decode the control region.
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 (2011-07) / 3GPP TS 22.368 version 10.5.0 Release 10)
[1]·
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 QAM16 or QAM64) on the radio interface which can require more complex and
expensive radio transceivers to implement.
It is usually justified to include such complex transceivers in a smartphone as a smartphone
will typically require a powerful processor to perform typical smartphone type functions. However, as
indicated above, there is now a desire to use relatively inexpensive and less complex devices to
communicate using LTE type networks. In parallel with this drive to provide network accessibility to
devices having different operational functionality, e.g. reduced bandwidth operation, there is a desire
to optimise the use of the available bandwidth in a telecommunications system supporting such
devices.
In many scenarios, providing low capability terminals such as those with a conventional highperformance
LTE receiver unit capable of receiving and processing (control) data from an LTE
downlink frame across the full carrier bandwidth can be overly complex for a device which only needs
to communicate small amounts of data. This may therefore limit the practicality of a widespread
deployment of low capability MTC type devices in an LTE network. It is preferable instead to provide
low capability terminals such as MTC devices with a simpler receiver unit which is more
proportionate with the amount of data likely to be transmitted to the terminal.
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. 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 allocation 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 also set out here. In providing this overview, 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 sub-carriers) 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 4 is a schematic diagram of a grid which illustrates the structure of a downlink LTE
sub-frame with a virtual carrier 401 occupying the resource blocks centred on the host carrier centre
frequency. The virtual carrier central frequency 403 is selected to be the central frequency 401 of the
host carrier.
In keeping with a conventional LTE downlink sub-frame illustrated in Figure 3A, the first n
symbols form the control region 300 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 401 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 (e.g. the PSS, SSS, and PBCH in the central band
310 in Figure 3A) are maintained. The virtual carrier is configured to interweave rather than clash
with such host carrier resources.
As can be seen from Figure 4, data transmitted on the virtual carrier 401 is transmitted across
a limited bandwidth. This might be any suitable bandwidth smaller than that of the host carrier. In the
example shown in Figure 4, the virtual carrier is transmitted across a bandwidth comprising 12 blocks
of 12 sub-carriers (i.e. 144 sub-carriers), which is equivalent to a 2.16MHz transmission bandwidth.
Accordingly, a terminal using the virtual carrier 401 need only be equipped with a receiver capable of
receiving and processing data transmitted over a bandwidth of 2.16MHz. This enables low capability
terminals (for example MTC type terminals) to be provided with simplified receiver units yet still be
able to operate within an OFDM type communication network which, as explained above,
conventionally requires terminals to be equipped with receivers capable of receiving and processing an
OFDM signal across the entire bandwidth of the signal.
As explained above, in OFDM-based mobile communication systems such as LTE, downlink
data is dynamically assigned to be transmitted on different sub-carriers on a sub-frame by sub-frame
basis. Accordingly, in every sub-frame, the network signals which sub-carriers on which symbols
contain data relevant to which terminals (i.e. downlink grant signalling).
As can be seen from Figure 3A, in a conventional downlink LTE sub-frame this information is
transmitted on the PDCCH during the first symbol or symbols of the sub-frame. However, as
previously explained, the information transmitted in the PDCCH is spread across the entire bandwidth
of the sub-frame and therefore cannot be received by a mobile communication terminal with a
simplified receiver unit capable only of receiving the reduced bandwidth virtual carrier. Accordingly,
certain predefined symbols (e.g. the final m symbols, where m is a positive integer) of the virtual
carrier can be reserved as a control region for the virtual carrier for the transmission of control data
indicating which resource elements of the virtual carrier 401 have been allocated to user equipment
(UEs) using the virtual carrier.
As the virtual carrier 401 is located within the centre band 310 of the downlink sub-frame, the
impact on host carrier PDSCH resources caused by the introduction of the virtual carrier within the
host carrier bandwidth is reduced since the resources occupied by the PSS, SSS and PBCH would be
contained within the virtual carrier region 401 and not the remaining host carrier PDSCH region.
It has been seen as desirable to extend the concept of virtual carriers to blocks of OFDM
subcarriers that are not centred on the host carrier central frequency. As previously mentioned, co
pending patent application number GB 1113801.3 [11] describes one arrangement where there is a
plurality of MTC devices and the central frequency of at least some of the virtual carriers is not same
as the central frequency of the host carrier.
Figure 5 illustrates this arrangement. A LTE downlink sub-frame is shown with a plurality of
virtual carriers outside of the control region 300, the data region includes a group of resource elements
positioned below the central band 310 which form a virtual carrier VC3 501. The virtual carrier VC3
501 is adapted so that data transmitted on the virtual carrier VC3 501 can be treated as logically
distinct from data transmitted in the remaining parts of the host carrier and can be decoded without
decoding all the control data from the control region 300.
Figure 5 also shows virtual carriers occupying frequency resources above the centre band
(VC1, 502) and (as in the situation illustrated in Figure 4) including the centre band (VC2, 401).
Therefore, depending on, for example, the expected virtual carrier throughput, the location of
a virtual carrier can be appropriately chosen to either exist inside or outside the centre band 310
according to whether the host or virtual carrier is chosen to bear the overhead of the PSS, SSS and
PBCH. This band allocation method for multiple VCs has particular application when terminals (UEs)
using the VC create a significant quantity of traffic at a given time.
However, in respect of this latter case, it has been recognised that the impact of the allocation
to non-central virtual carriers upon terminal receivers having direct conversion mechanism needs to be
considered.
As noted previously, direct conversion receiver architectures are convenient for manufacturers
and are widely used in conventional 3G mobile phones. This receiver architecture converts (carrier
modulated) radio frequency (RF) signals to baseband (BB) signals, i.e. the "modulating" signal
typically at frequencies close to OHz, directly without intermediate frequency (IF).
Figure 6A illustrates the general architectural scheme of a Direct Conversion receiver unit.
An RF signal is received by an amplifier 601 from an antenna arrangement (not shown). The
amplifier 601 applies a gain to the received RF signal. A local oscillator 603, set at the RF carrier
frequency, generates an oscillator signal that is mixed with the received RF signal in a mixer 602,
thereby down-converting the received RF signal to a base band signal.
Direct Conversion makes possible an architecture that is simple and that requires a reduced
number of RF parts (when compared with alternatives such as the heterodyne receiver arrangement
with IF filter described below). In terms of cost saving and size reduction, the direct conversion
architecture is preferable for MTC type devices.
Figure 6B illustrates this down-conversion from RF to BB frequencies and identifies a known
vulnerability of Direct Conversion - self-mixing. If a receiver is imperfect (more likely in the case of
low-cost, small form-factor devices), local-oscillator (LO) leakage may occur. The signal generated
by the local oscillator 603 may interfere with the signal received at the amplifier 601 and/or the
received RF signal provided to the mixer 602. This causes a phenomenon known as "DC offset",
where DC stands for Direct Current. A helpful description of the causes of DC offset may be found at
reference [10].
Alternatives to direct conversion do exist - as the name implies an "indirect" conversion
mechanism may be applied. One such alternative is the heterodyne architecture illustrated in Figure 7 :
here radio frequency is converted to an intermediate frequency (IF) before then being converted to
baseband, the IF being selected to facilitate filtering out of any DC offset components.
There is no IF filter to remove DC offset in a direct conversion architecture (indeed the
alternative name for the architecture is "zero-IF").
The DC offset disrupts the demodulation of symbols at the centre frequency of the host
carrier, i.e. those frequencies which when converted to BB are close to OHz. While conventional error
correction techniques could be applied to address this disruption (see the remarks below concerning
"puncturing"), if direct conversion is to be adopted in significant numbers of terminal devices, the best
way to avoid the disturbance by DC offset is avoid using the centre frequency for data allocation.
It is for this reason that (as may be seen from the relevant equation in 3GPP 36.211 V8.4.0
section 6.12) LTE defines a baseband signal that has no component at its centre frequency): in other
words, LTE has a subcarrier to which no data may be allocated at its host carrier centre frequency.
More generally, OFDM based radio access systems typically feature a subcarrier upon which no
information is sent. This unused subcarrier is conventionally referred to as a "DC subcarrier", the DC
again standing for "direct current".
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
[ 1 1]: this camp-on process is incorporated herein by reference.
As described in GB 1113801.3 [11], both "conventional LTE" and virtual carrier
implementations could conveniently include location information for the virtual carrier within the
PBCH, which already carries the Master Information Block (MIB) in the host carrier centre band.
Alternatively, virtual carrier location information could be provided in the centre band, but outside of
the PBCH. It can for example be always provided after and adjacent to the PBCH. By providing the
location information in the centre band but outside of the PBCH, the conventional PBCH is not
modified for the purpose of using virtual carriers, but a virtual carrier terminal can easily find the
location information in order to detect the virtual carrier, if any.
While the virtual carrier location information, if provided, can be provided elsewhere in the
host carrier, it may be advantageous to provide it in the centre band, for example because a virtual
carrier terminal may configure its receiver to operate on 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
[11].
In low traffic conditions, the allocation of a new unused sub-carrier for each new virtual
carrier (illustrated in Figure 5) is adequate. Conveniently, an additional DC subcarrier (unused subcarrier)
is allocated by a base station at the centre frequency of each virtual carrier as that virtual
carrier is established.
In the "simple" Figure 5 example, virtual carrier VC2 has the same centre frequency as the
host carrier. The respective centre frequencies for virtual carriers VC1 and VC3 are different from the
centre frequency of host carrier (and VC2).
The base station allocating sub-carriers includes a radio resource management (RRM) unit and
a scheduler. The RRM decides the centre frequency of VC for a MTC UE while the scheduler
allocates the DC subcarrier (unused subcarrier) at that VC centre frequency.
Figure 8A illustrates the logical steps taken by the RRM for deciding centre frequency:
1. Check the number of existing MTC UEs camped on the base station
2 . Check the traffic (active state) of each VC
3. Estimate the available capacity in each VC
4 . Select the best VC (e.g. the VC having the highest available capacity)
5 . Indicate a decided VC position to UE by RRC protocol.
[The indication by higher layer (camp on process) is discussed in greater depth above]
6 . Indicate a decided VC position to scheduler inside base station.
Figure 8B illustrates the logical steps taken by the scheduler as it allocates an unused (DC)
subcarrier allocation:
1. Receive the VC position from RRM
2 . Obtain the transmit data from queue.
3 . Obtain the feedback information from UE.
a . channel quality information(CQI)
b. scheduling request(SR)
4 . Decide the frequency resources required to transmit data (i.e. subcarriers) except centre
frequency
5. Modulate each symbol
6 . Transmit control channel(VC-PDCCH)
7 . Transmit data channel(VC-PDSCH)
Figure 8C illustrates the operation of a terminal in the VC allocation scheme of Figure 5 :
1. Receive the VC position by higher layer (e.g. RRC message)
2 . Change the VC centre frequency.
3 . Wait for the VC-PDCCH.
4 . Receive the VC-PDSCH
5. Send acknowledgements when successful (ACK)/unsuccessful (NACK)
A new MTC UE architecture for narrow band (i.e. virtual carrier operation) has been proposed
in the relevant 3GPP standard. The proposed new architecture seeks to permit an RF bandwidth
capability that is different from the baseband one. In one particular proposal, the RF bandwidth in
MTC terminal is same as host carrier bandwidth (e.g. 20MHz), while the baseband processing is
narrow band (e.g. 1.4MHz): i.e. significantly narrower than the host carrier bandwidth.
For the sake of convenience, the combination of narrow band for both RF and baseband is
referred to hereafter as "Normal narrow band" or "type A" architecture: a combination of narrow band
for only Baseband and "full" - i.e. same as HC - bandwidth for RF is termed "Baseband narrow band"
or just "type B" architecture. The operational frequency bands for these two types of RF receiver
architecture are illustrated in Figure 9 . The type A architecture (910) requires that control signals and
data are all transmitted for a virtual channel on the relevant narrow band. The type B architecture
(920) requires instead that the receiver operates on the full bandwidth for RF.
Variants of the type B architecture are contemplated - see Figure 10. As may be seen from
the illustrations of the LTE downlink sub-frame - Figs 3A, 4 and 5 - the user plane data is transmitted
in different symbols (i.e. at different times) from the control data whereby radio communication is
established and maintained. Type A architectures are referred to as Option DL-1 .
In a first variant of the type B architecture, Option DL-2, control and data channels are
received in the baseband in narrowband.
In another variant of the type B architecture, Option DL-3, control channels are received in the
baseband at full bandwidth while narrowband operation is reserved for the data channel.
One benefit of the type B (Baseband narrow band) architectures is that there is no need for a
DC subcarrier for VCs located away from the HC centre frequency because the VC centre frequency is
same as LTE HC centre frequency in terms of direct conversion.
In this regard it is worth noting that direct conversion is a function of RF transceiver large
scale integrated (LSI) circuitry (see the inset portion of Figure 6), not of the baseband unit.
Problems may arise when both Normal narrow band (type A) terminals and Baseband narrow
band (type B) terminals operate under the same host carrier (the mixed operation case). In other
words, it would be desirable to maximize the benefit of "baseband narrow band" (type B) in the mixed
operation case.
Figure 11 illustrates the case where terminals of both types (A and B) make use of the same
host carrier.
In VCl', MTC UE is assumed to be type A, VC1' has its own DC subcarrier (DCsubcarrier
1): this corresponds to the "simple" case described above (in Figure 5) where an additional unused
sub-carrier is allocated at the centre frequency of each virtual carrier.
In VC2', MTC UE is also assumed to be type A, VC2' can reuse host carrier centre frequency.
As a large number of terminals are likely to use LTE host carrier centre frequency, this arrangement
may not be the most robust or effective, from a resource usage point of view.
In VC3', MTC UE is assumed to be type B. VC3' reuses the host carrier centre frequency and
is not provided with its own unused subcarrier: only a type B architecture can use such a VC without
exposing the UE to self-mixing. From a resource allocation point of view, this is efficient. This
means "baseband narrow band" (type B) device has an advantage in terms of flexibility of band
allocation for virtual carrier.
The base station in the mixed operation case described above is required to do more that for
the previous "simple" case. In particular it must discover the terminal RF capability before deciding
how to allocate virtual carrier capacity.
The base station must firstly determine the RF capability (e.g. RF bandwidth) for each
terminal. If that RF capability indicates a terminal of Baseband narrow band (type B), the base station
allocates the VCs for this terminal to non-centre frequency of host carrier where capacity permits. If
however, the detected RF capability indicates a terminal of Normal narrow band (type A), the base
station will allocate the VCs for this terminal to LTE centre frequency of host carrier as long as
capacity allows; otherwise the base station allocates remaining VCs (for type A terminals) to LTE
non-centre frequency of host carrier but requires that these VCs provide an unused subcarrier at their
centre frequency.
The terminal is thus required to: report its "bandwidth status" (e.g. RF capability and/or RF
bandwidth) to base station and to follow VC allocation instructions transmitted by the base station.
As previously, the base station includes a radio resource management (RRM) unit and a
scheduler. Again, the RRM decides the centre frequency of VC for a MTC UE while the scheduler
allocates the DC subcarrier (unused subcarrier) at that VC centre frequency.
Figure 12A illustrates the logical steps taken by the RRM for deciding centre frequency:
1. Determine the UE bandwidth status (RF capability) in advance (e.g. during RRC connection
setup)
2 . Check the number of existing MTC UEs camped on the base station.
3 . Check the traffic (active state) of each VC (e.g. how congested)
4 . Estimate the available capacity in each VC
5 . Select the best VC (e.g. the VC having the highest available capacity and best adapted to serve
a UE of the determined bandwidth status)
a . If terminal is Baseband narrow band (type B), a frequency other than original LTE
host carrier centre frequency is allocated for VC.
b. If terminal is normal narrow band (type A), original LTE host carrier centre frequency
is allocated for VC.
c . If terminal is normal narrow band (type A) and there is insufficient capacity at the
host carrier centre frequency, a frequency other than original LTE host carrier centre
frequency is allocated for VC.
6 . Indicate a decided VC position to UE by RRC protocol.
[The indication by higher layer (camp on process) is discussed in greater depth above]
7 . Indicate a decided VC position to scheduler inside base station.
The logical steps taken by the scheduler as it allocates an unused (DC) subcarrier allocation
are identical to those take in the "simple" case and described above in relation to Figure 8B:
1. Receive the VC position from RRM
2 . Obtain the transmit data from queue.
3. Obtain the feedback information from UE.
a . channel quality information (CQI)
b. scheduling request (SR)
4 . Decide the frequency resources required to transmit data (i.e. subcarriers) except centre
frequency
5. Modulate each symbol
6 . Transmit control channel(VC-PDCCH)
7 . Transmit data channel(VC-PDSCH)
As noted earlier, the key difference between the first "simple" and second "mixed operation"
cases is the requirement in the latter case for each terminal to report its own RF bandwidth capability
(bandwidth status) to the base station. Figure 12B illustrates the operation of a terminal in the VC
allocation scheme of Figure 11: this differs from the scheme illustrated in Figure 8C in the step for
reporting RF bandwidth capability. With that exception, the terminal follows the direction from base
station in the same manner as for the "simple" case.
1. Send the RF bandwidth capability information to base station (e.g. RRC connection setup)
2 . Receive the VC position by higher layer (e.g. RRC message)
3. Change the VC centre frequency.
4 . Wait for the VC-PDCCH.
5 . Receive the VC-PDSCH
6 . Send acknowledgements when successful (ACK)/unsuccessful (NACK)
Capability detection in the UE may comprise detection of whether the UE is in fact flagged as
an MTC-type device and only if it is will it be necessary to make any determination of RF capability
(non MTC-devices not typically needing access to the virtual carrier). Figure 12C shows one possible
arrangement where after determining that the device is of the MTC-type, it is queried whether the base
station (or associated core network entities such as the MME) has capability information for the UE: in
the absence of such information the base station may interrogate the UE to extract this information -
for example by forcing a location update event thereby ensuring that the UE reports its capabilities in
accordance with the standard.
Figure 13A illustrates the procedure by which terminals (UEs) report capability information to
the e-UTRAN network entities in LTE (e.g. REL8 LTE). At power on (or when the UE has recently
entered the area of coverage of a base station controlling entity - i.e. the MME), the UE and MME
exchange a number of signals to "attach" the UE to the relevant MME and to assign a suitable base
station (eNodeB) to the UE. Part of the exchange of signals includes a message from the base station
to the UE requesting UE capability information. In response, the UE prepares a message in
accordance with a standardised System Information Block (SIB) including an information element
(IE) of known format. The IE in turn provides a data structure in which the UE capability may be
reported. The details of the 3GPP standard procedure for transmitting UE capability information may
be found at 3GPP TS 36.331 V8.12.0 at section 5.6.3. The UECapabilitylnformation message
described there takes a specific form - each UE capability IE being stored under an UE-Capability
RAT-Container. The capability IE of an MTC-type UE may be treated as part of the LTE capability
(see TS36.306) or as if it belonged to an independent RAT.
Figure 13B illustrates a conventional UE-EUTRA-Capability IE into which new IEs relevant
to MTC-type devices may be incorporated.
A number of different new IEs may be considered for the purpose of facilitating the reporting
of the RF/BB capability of UEs so that certain aspects of the invention may be implemented. While
referred to as "bandwidth status", these new IEs may not actually include information directly relevant
to bandwidth but rather may serve as indications of the expected bandwidth capabilities of the UE.
Examples of new information elements for appending to the conventional UE-EUTRA-Capability IE
structure (or to some similar structure that serves to report UE capability) include:
a . "NarrowbandOption" - an IE that takes values corresponding to the different options for
downlink bandwidth architecture as illustrated in Figure 10.
b. "MTC bandwidth" - an IE that includes fields for characterising the bandwidth size for
each of the RF, BB and the data-only part of the BB in terms of resource blocks
( 180kHz), subcarriers (15kHz) or in units of MHz
c . "Receiver ArchitectureOption" - an IE that takes values corresponding to the type of
receiver architecture the UE uses - IF conversion or Direct conversion
d . "CentreFrequencyAllocationUEPreference" - an IE within a UE Preference Options
structure that takes values corresponding to an indication of whether an allocated centre
frequency for that UE is preferred to be "unused" or "used"
Embodiments of the invention may in particular be employed within the context of what might
be termed "virtual carriers" operating within a bandwidth of one or more "host carriers". The concepts
of virtual carriers are described in co-pending UK patent applications numbered 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. The
reader is referred to these co-pending applications for more details, but for ease of reference an
overview of the concept of virtual carriers is also provided here.
Figure 14 provides a schematic diagram showing part of an adapted LTE mobile
telecommunication system arranged in accordance with an example of the present invention. The
system includes an adapted enhanced Node B (eNB) 1401 connected to a core network 1408 which
communicates data to a plurality of conventional LTE terminals 1402 and reduced capability terminals
1403 within a coverage area (cell) 1404. Each of the reduced capability terminals 1403 has a
transceiver unit 1405 which includes a receiver unit capable of receiving data across a reduced
bandwidth (i.e. narrowband) and a transmitter unit capable of transmitting data across a reduced
bandwidth when compared with the capabilities of the transceiver units 1406 included in the
conventional LTE terminals 1402.
The adapted eNB 1401 is arranged to transmit downlink data using a sub-frame structure that
includes a virtual carrier as described with reference to Figure 11. The task of assigning reduced
capacity terminals 1403 to a given virtual carrier is performed by a radio resource management (RRM)
unit 1411 within the eNB 1401. Data is then transmitted to reduced capability terminals 1403 by an
adapted scheduling unit 1409 in the eNB. The reduced capability terminals 1403 are thus able to
receive and transmit data using the downlink virtual carriers as described above.
As has been explained above, because the reduced complexity terminals 1403 receive and
transmit data across a reduced bandwidth on the uplink and downlink virtual carriers, the complexity,
power consumption and cost of the transceiver unit 1405 needed to receive and decode downlink data
and to encode and transmit uplink data is reduced compared to the transceiver unit 1406 provided in
the conventional LTE terminals.
When receiving downlink data from the core network 1408 to be transmitted to one of the
terminals within the cell 1404, the adapted eNB 1401 is arranged to queue that data in a queue 1410
and to determine if the data is bound for a conventional LTE terminal 1402 or a reduced capability
terminal 1403. This can be achieved using any suitable technique. For example, data bound for a
reduced capability terminal 1403 may include a virtual carrier flag indicating that the data must be
transmitted on the downlink virtual carrier. If the adapted eNB 1401 detects that downlink data is to be
transmitted to a reduced capability terminal 1403, an adapted scheduling unit 1409 included in the
adapted eNB 1401 ensures that the downlink data is transmitted to the reduced capability terminal in
question on the downlink virtual carrier. In another example the network is arranged so that the virtual
carrier is logically independent of the eNB. More particularly the virtual carrier may be arranged to
appear to the core network as a distinct cell so that it is not known to the core network that the virtual
carrier has any relationship with the host carrier. Packets are simply routed to/from the virtual carrier
just as they would be for a conventional cell.
In another example, packet inspection is performed at a suitable point within the network to
route traffic to or from the appropriate carrier (i.e. the host carrier or the virtual carrier).
In yet another example, data from the core network to the eNB is communicated on a specific
logical connection for a specific terminal device. The eNB is provided with information indicating
which logical connection is associated with which terminal device. Information is also provided at the
eNB indicating which terminal devices are virtual carrier terminals and which are conventional LTE
terminals. This information could be derived from the fact that a virtual carrier terminal would initially
have connected using virtual carrier resources.
Virtual carrier terminals are arranged to indicate their capability to the eNB during the
connection procedure. Accordingly the eNB can map data from the core network to a specific terminal
device based on whether the terminal device is a virtual carrier terminal or an LTE terminal.
In some examples, the virtual carrier inserted within the host carrier can be used to provide a
logically distinct "network within a network". In other words data being transmitted via the virtual
carrier can be treated as logically and physically distinct from the data transmitted by the host carrier
network. The virtual carrier can therefore be used to implement a so-called dedicated messaging
network (DMN) which is "laid over" a conventional network and used to communicate messaging
data to DMN devices (i.e. virtual carrier terminals).
It will be appreciated that various modifications can be made to the embodiments described
above without departing from the scope of the present invention as defined in the appended claims. In
particular although embodiments of the invention have been described with reference to an LTE
mobile radio network, it will be appreciated that the present invention can be applied to other forms of
network such as GSM, 3G / UMTS, CDMA2000, etc. The term MTC terminal as used herein can be
replaced with user equipment (UE), mobile communications device, terminal device etc. Furthermore,
the term base station refers to any wireless network entity that provides UEs with an air interface to a
cellular telecommunications network: while the term has been used interchangeably with e-NodeB in
the foregoing it should be understood that it encompasses equivalent network entities in LTE and
alternative radio access architectures including: eNode-Bs; Node-Bs, pico-, femto- and micro base
station equipment, relays; boosters etc..
The term "unused subcarrier" is used interchangeably with "DC sub carrier" however it
encompasses the concept of leaving a subcarrier without data. A subcarrier may be left unused in a
number of ways and a different term may be adopted to express the precise manner of "unuse". Figure
15 illustrates two possible ways of leaving a subcarrier effectively unused. Thus a subcarrier may be
ignored by a scheduler entirely scheduling data into other subcarriers but not into an un-scheduled
(and thereby "unused") subcarrier: in Figure 15, data packets A, B, C and D are allocated to the first,
second, fourth and fifth symbols - and no data is scheduled for the third symbol.
Alternatively, the scheduler may initially allocate data for the subcarrier in question but the
subcarrier is not transmitted: i.e. the allocated data is dropped in an operation known as "puncturing".
In Figure 15, this is illustrated by showing the third of five symbols empty but data packets A, B, D
and E allocated to the first, second, fourth and fifth symbols. Data packet C is scheduled but not
carried. As the term implies, puncturing entails the receiving terminal receiving incomplete data (the
data originally scheduled at the punctured subcarrier is missing). The missing data can however be
reconstructed using conventional error correction techniques such as forward error correction (FEC).
It will also be appreciated that although the above description of a scheme in which host
carriers and virtual carriers are supported by geographically separated base stations has primarily
focussed on downlink transmissions by way of example, the same concepts can equally be applied for
uplink transmissions: in particular, where VC centre frequency in uplink is same as HC centre
frequency in uplink.
Further particular and preferred aspects of the present invention are set out in the
accompanying independent and dependent claims. It will be appreciated that 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.
Various aspects and features are defined in the following numbered clauses:
1. A terminal having:
a radio-frequency, RF, receiving portion for receiving RF signals from a base station, the RF
receiving portion having an associated bandwidth status, said bandwidth status defining to which
mode of virtual channel operation the terminal device is to be assigned;
a capability reporting unit adapted to determine the bandwidth status of the RF receiving
portion of the terminal device; and
an RF transmitting portion for communicating control data to the base station, wherein the
control data includes the bandwidth status.
2 . A terminal according to clause 1, wherein the bandwidth status is a classification of
terminal RF receiving portion architecture selected from a group including: intermediate frequency
conversion, direct conversion, normal narrowband and baseband narrowband.
3. A terminal according to clause 1 or 2, wherein the bandwidth status corresponds to at
least one parameter characterising the bandwidth size capability of the terminal RF receiving portion.
4 . A terminal according to any of clauses 1 to 3, wherein the terminal and base station
communicate data in a wireless telecommunications system using a first plurality of Orthogonal
Frequency Division Multiplex, OFDM, sub-carriers spanning a first frequency bandwidth, at least one
of said subcarriers being an unused centre frequency for the first frequency bandwidth, and wherein
the mode of virtual channel operation relates to a virtual channel, the virtual channel being a group of
sub-carriers selected from said first plurality of OFDM sub-carriers and spanning a second frequency
bandwidth, said second frequency bandwidth being substantially narrower than the first frequency
bandwidth.
5 . A terminal according to clause 4, wherein the terminal has a first bandwidth status,
first bandwidth status representing an indication that the terminal has a receiver that can receive radio
frequency, RF, signals over the first frequency bandwidth and baseband signals over the second
frequency bandwidth.
6 . A terminal according to clause 4, wherein the terminal has a second bandwidth status,
second bandwidth status representing an indication that the terminal has a receiver that can receive
radio frequency, RF, signals and baseband signals over the second frequency bandwidth.
7 . A terminal according to any of clauses 1 to 6, wherein the bandwidth status represents
an indication of a classification of receiver architecture selected from a group including: intermediate
frequency conversion, direct conversion, normal narrowband and baseband narrowband.
8. A terminal according to any preceding clause, wherein the bandwidth status
corresponds to at least one parameter characterising the bandwidth size capability of the receiver.
9 . A method for communicating control data from a terminal device having a radiofrequency,
RF, receiving portion to a base station in a wireless telecommunications system using a
first plurality of Orthogonal Frequency Division Multiplex, OFDM, sub-carriers spanning a first
frequency bandwidth, the RF receiving portion having an associated bandwidth status, the method
comprising:
determining the bandwidth status of the RF receiving portion of the terminal device;
transmitting control data to the base station, wherein the control data includes the bandwidth
status; and
receiving RF signals from the base station using a mode of virtual channel operation assigned
in accordance with the bandwidth status.
10. A method according to clause 9, wherein the mode of virtual channel operation relates
to a virtual channel, the virtual channel being a group of sub-carriers selected from said first plurality
of OFDM sub-carriers and spanning a second frequency bandwidth, said second frequency bandwidth
being substantially narrower than the first frequency bandwidth.
REFERENCES
[I] ETSI TS 122 368 V10.530 (201 1-07) / 3GPP TS 22.368 version 10.5.0 Release 10)
[2] UK patent application GB 1101970.0
[3] UK patent application GB 1101981.7
[4] UK patent application GB 1101966.8
[5] UK patent application GB 1101983.3
[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] DCoffset primer
{http://venividnviki.ee. i i
[I I] UK patent application GB 1113801.3
CLAIMS
1. A terminal having:
a radio-frequency, RF, receiving portion for receiving RF signals from a base station, the RF
receiving portion having an associated bandwidth status, said bandwidth status defining to which
mode of virtual channel operation the terminal device is to be assigned;
a capability reporting unit adapted to determine the bandwidth status of the RF receiving
portion of the terminal device; and
an RF transmitting portion for communicating control data to the base station, wherein the
control data includes the bandwidth status.
2 . A terminal as claimed in claim 1, wherein the bandwidth status is a classification of
terminal RF receiving portion architecture selected from a group including: intermediate frequency
conversion, direct conversion, normal narrowband and baseband narrowband.
3 . A terminal as claimed in claim 1, wherein the bandwidth status corresponds to at least
one parameter characterising the bandwidth size capability of the terminal RF receiving portion.
4 . A terminal as claimed in claim 1, wherein the terminal and base station communicate
data in a wireless telecommunications system using a first plurality of Orthogonal Frequency Division
Multiplex, OFDM, sub-carriers spanning a first frequency bandwidth, at least one of said subcarriers
being an unused centre frequency for the first frequency bandwidth, and wherein the mode of virtual
channel operation relates to a virtual channel, the virtual channel being a group of sub-carriers selected
from said first plurality of OFDM sub-carriers and spanning a second frequency bandwidth, said
second frequency bandwidth being substantially narrower than the first frequency bandwidth.
5 . A terminal as claimed in claim 4, wherein the terminal has a first bandwidth status,
first bandwidth status representing an indication that the terminal has a receiver that can receive radio
frequency, RF, signals over the first frequency bandwidth and baseband signals over the second
frequency bandwidth.
6 . A terminal as claimed in claim 4, wherein the terminal has a second bandwidth status,
second bandwidth status representing an indication that the terminal has a receiver that can receive
radio frequency, RF, signals and baseband signals over the second frequency bandwidth.
7 . A terminal as claimed in Claim 1, wherein the bandwidth status represents an
indication of a classification of receiver architecture selected from a group including: intermediate
frequency conversion, direct conversion, normal narrowband and baseband narrowband.
8. A terminal as claimed in Claim 1, wherein the bandwidth status corresponds to at
least one parameter characterising the bandwidth size capability of the receiver.
9 . A method for communicating control data from a terminal device having a radiofrequency,
RF, receiving portion to a base station in a wireless telecommunications system using a
first plurality of Orthogonal Frequency Division Multiplex, OFDM, sub-carriers spanning a first
frequency bandwidth, the RF receiving portion having an associated bandwidth status, the method
comprising:
determining the bandwidth status of the RF receiving portion of the terminal device;
transmitting control data to the base station, wherein the control data includes the bandwidth
status; and
receiving RF signals from the base station using a mode of virtual channel operation assigned
in accordance with the bandwidth status.
10. A method as claimed in claim 9, wherein the mode of virtual channel operation relates
to a virtual channel, the virtual channel being a group of sub-carriers selected from said first plurality
of OFDM sub-carriers and spanning a second frequency bandwidth, said second frequency bandwidth
being substantially narrower than the first frequency bandwidth.