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Title of the Invention
WIRELESS COMMUNICATION SYSTEMS
Field of the Invention
The present invention relates to wireless communication systems, more
particularly packet-based systems in which a base station (BS) communicates with
multiple fixed or mobile subscriber stations (SS).
Background of the Invention
Recently, various standards have been developed for data communication over
broadband wireless links. One such standard is set out in the IEEE 802.16
specifications and is commonly known as WiMAX. The specifications include IEEE
802.16-2004, primarily intended for systems having fixed subscriber stations, and an
enhanced specification IEEE 802.16e-2005 which among other things provides for
mobile subscriber stations. In the following description, the term subscriber station (SS)
applies to both fixed and mobile stations (SS/MS).
The entire content of IEEE Std 802.16-2004 "Air Interface for Fixed Broadband
Wireless Access Systems" is hereby incorporated by reference. IEEE 802.16
envisages single-hop systems in which the subscriber station communicate directly with
a base station within range, the range of a base station defining a "cell". By deploying
multiple base stations at suitable positions within a given geographical area, a
contiguous group of cells can be created to form a wide-area network. In this
specification, the terms "network" and "system" will be used equivalently.
In systems of the above type, data is communicated by exchange of packets
between the subscriber stations and base station whilst a connection (management

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connection or transport connection) is maintained between them. The direction of
transmission of packets from the subscriber station to the base station is called the
uplink, and the direction from the base station to the subscriber station is the downlink.
The packets have a defined format which follows a layered protocol applied to the
system and its component radio devices. Protocol layers relevant to packets as such
are the so-called physical layer (PHY) and media access layer (MAC). In the IEEE
802.16-2004 specification, these protocol layers form a protocol "stack" as shown in Fig.
1. Incidentally, Fig. 1 also shows interfaces between protocol layers in the form of
service access points (SAPs), though these are not relevant to the present invention.
The media access layer is responsible for handling network access, bandwidth
allocation, and maintaining connections. This includes controlling access of the BS and
SSs to the network on the basis of "frames" which are divided into a number of slots.
Data is exchanged between the MAC peer entities, in other words, between the
subscriber station and base station, in units of a protocol data unit (PDU), the PDU
being conveyed across the PHY layer using a number of slots. The MAC is divided into
sublayers including a security sublayer (see Fig. 1) for allowing authentication, key
exchange and encryption of PDUs.
Various physical layer implementations are possible in a IEEE 802.16 network,
depending on the available frequency range and application; for example, both a time
division duplex (TDD) mode - in which uplink and downlink transmissions are separated
in time but may share the same frequency - and a frequency division duplex (FDD)
mode - where uplink and downlink transmissions can occur at the same time but on
different frequencies - are possible. The PHY layer also defines the transmission
technique such as OFDM (orthogonal frequency division multiplexing) or OFDMA
(orthogonal frequency division multiple access). A connection between a base station
and subscriber station (more precisely, between MAC layers in those devices - so-

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called peer entities) is assigned a connection ID (CID) and the base station keeps track
of CIDs for managing its active connections.
The concept of quality of service (QoS) is employed in wireless communication
systems for allowing a wide range of services to be provided. During communication
with a subscriber station, the base station allocates a QoS level depending on the type
of service requested by the subscriber station and available bandwidth, bearing in mind
that the base station typically will be communicating with several subscriber stations
simultaneously. The QoS is allocated first during a network entry procedure at the time
the subscriber station joins the network, and may be modified subsequently by the
subscriber station making a request to the base station whilst the connection is
maintained.
The relationship between QoS and CID/SFID is illustrated in Figure 2. For ease
of understanding Fig. 2, it is noted that "service flow" refers to transmission of data in a
given direction (uplink or downlink) on a connection having a particular QoS. The QoS
of the connection is defined by a service flow identifier (SFID) which has a one-to-one
relationship to the connection ID.
For example, the IEEE 802.16 specification provides four QoS classes or levels
as follows:
(i) Unsolicited Grant Service (UGS):
This service supports real-time data streams consisting of fixed-size packets
issued at periodic intervals, such as voice calls (VoIP).
(ii) Real-time Polling Service (rtPS):
This supports real-time data streams consisting of variable-sized packets issued
at periodic intervals, such as MPEG video.
(iii) Non-real-time Polling Service (nrtPS):

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A service level intended to support delay-tolerant data streams consisting of
variable-sized packets for which a minimum transfer rate is needed, such as FTP (File
Transfer Protocol).
(iv) Best Effort (BE)
This lowest service level is for data streams with no particular service
requirements. Packets are handled as and when bandwidth is available.
However efficient the communication scheme employed in terms of use/re-use of
available frequencies, since several subscriber stations typically access the same base
station at the same time there is the possibility of "collision" between accesses from the
subscriber stations. A contention-based scheme is therefore adopted in which the QoS
is used to allocate bandwidth among the connected subscriber stations.
As already mentioned, packets involve both PHY and MAC protocol layers. More
particularly, Figure 3 shows a packet format having two parts, a PHY header and a
MAC PDU. The MAC PDU in turn consists of a MAC header, an optional payload, and
optional error correction code (cyclic redundancy code or CRC). The PHY header
includes training sequences, frequency band allocation information, and other
information relating to physical layer parameters. Within the MAC PDU, the MAC
header normally gives essential parameters for media access, such as the type of PDU,
MAC address, and type of MAC signalling etc. The CRC within MAC PDU is optional,
and can be used to check the received MAC PDU. The payload within MAC PDU is
also optional. For example, some controlling messages, such as a bandwidth request,
or an ACK message, have no payload. The payload could be data from higher layer, or
sub-MAC-header, which can give additional MAC information.
To support addressing and QoS control, some wireless communication systems
put connection identification (CID) into MAC header. For instance, in WiMAX, the
service flow between SS/MS and BS can be created and activated during network entry

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procedure or by dynamic service flow procedure. As mentioned earlier, a service flow
ID (SFID) will be assigned to each existing service flow, and each service flow is also
associated to a specific QoS demand. A service flow has at least an SFID and an
associated direction. The connection ID (CID) of the transport connection exists only
when the service flow is admitted or active. The relationship between SFID and
transport CID is unique, which means an SFID never be associated with more than one
transport ID, and a transport CID shall never be associated with more than one SFID.
Figure 4 shows a generic MAC header format as specified in IEEE 802.16-2004,
including a 16-bit CID.
In single hop wireless communication systems (e.g. IEEE802.16-2004 and
IEEE802.16e-2005 as mentioned above), each subscriber station (SS or MS) can
communicate with the base station (BS) directly. Recently, efforts are being made to
extend IEEE 802.16 to multi-hop configurations in which traffic between BS and SS is
routed via one or more relay stations (RS), rather than being transmitted directly.
Figure 5 shows an example of such a configuration having two relay stations labelled
RS1# and RS2#. If the network is modified to support relaying functionality as shown in
Fig. 5, normally, the relay station (RS) will relay all the packets from the radio devices
(SSs or other RSs) within its coverage, to the BS.
The problem of this protocol is that the RS will also need to relay the PHY header
in each instance, which may cost a lot of bandwidth between RS and BS. Especially,
when several RSs are present, forming a chain of links between the BS and SSs, the
PHY overhead between BS and its closest RS, such as RS 1# in Fig. 5, will
accumulate, and more bandwidth will be used for PHY signalling overhead. This is a
particular problem since typically bandwidth is more constrained on the uplink than on
the downlink.

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Summary of the Invention
According to a first aspect of the present invention, there is provided a wireless
communication method in a system in which subscriber stations are each operable for
communication with a base station, the base station being capable of performing
simultaneous communications with a plurality of the subscriber stations simultaneously
by exchange of packets each conforming with a layered protocol of said system, the
packets comprising a first portion for defining physical layer (PHY) parameters and a
second portion for defining media access layer (MAC) parameters, and
communications between the subscriber stations and the base station being performed
wholly or partly through at least one relay station, the method comprising steps of, in
the relay station: receiving a plurality of packets from the subscriber stations; detecting
the second portion of each of the packets; combining the detected second portions to
form a second portion of at least one new packet; and transmitting the new packet to
the base station.
Preferably, the method further comprises, in the relay station, categorising the
detected second portions of the received packets, and in said combining step forming a
new packet for each category. The categorising step may be performed based on type
or service level information contained in each second portion of the received packets
According to a second aspect of the present invention, there is provided a relay
station for use in a wireless communication method in a system in which subscriber
stations are each operable for communication with a base station, the base station
being capable of performing simultaneous communications with a plurality of the
subscriber stations simultaneously by exchange of packets each conforming with a
layered protocol of said system, the packets comprising a first portion for defining
physical layer (PHY) parameters and a second portion for defining media access layer

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(MAC) parameters, and communications between the subscriber stations and the base
station being performed wholly or partly through the relay station, the relay station
comprising: means for receiving a plurality of packets from the subscriber stations;
means for detecting the second portion of each of the packets; means for combining
the detected second portions to form a second portion of at least one new packet; and
means for transmitting the new packet to the base station.
Other aspects of the invention provide a wireless communication system, a base
station, a computer program (which may be stored on a computer-readable recording
medium), and a packet format as set forth in the accompanying independent claims.
Brief Description of the Drawings
Reference is made, by way of example only, to the accompanying drawings in
which:
Figure 1 shows protocol layering in accordance with IEEE 802.16;
Figure 2 shows the relationship between CID, SFID and QoS in an IEEE 802.16
network;
Figure 3 shows a packet format capable of being used in an IEEE 802.16
network;
Figure 4 shows a generic MAC header of a packet as set forth in the IEEE 802.16
specification;
Figure 5 illustrates a simple relay protocol in a multi-hop wireless communication
system;
Figure 6 illustrates the relay protocol employed in the present invention;
Figure 7 is a flowchart of processing in an RS to combine MAC PDUs;
Figure 8 shows a first method of combining MAC PDUs;
Figure 9 shows a second method of combining MAC PDUs;

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Figure 10 shows a third method of combining MAC PDUs; and
Figure 11 is a flowchart of processing in a BS.
Detailed Description
An embodiment of the present invention will now be described with reference to
Fig.s 6-11, using an IEEE 802.16 network as an example.
In this invention, an algorithm is proposed by which the RS can combine the
packets received from the communication devices connected to itself, forming one or
more new packets (combined packets), and send the combined packets to the BS (or to
an upstream RS), thus decreasing the overhead and collision of packet transmission.
This relay protocol is schematically shown in Fig. 6. There are various possible ways of
combining received packets, as will now be explained.
1. Operations in RS
Referring to Fig. 7, the following operations take place on the RS side after the
RS receives multiple packets from the connected radio devices.
(i) RS detaches the MAC PDUs from the packets received. If the CRC is available
in a MAC PDU, then RS will check the CRC and discard the MAC PDUs with CRC
error.
(ii) In terms of the types or the QoS level of the received MAC PDUs, the RS then
categorises the correctly received MAC PDUs. The purpose of this step is to further
decrease the overhead by combining MAC PDUs, and to make the QoS management
convenient in RS. For example, the received packets may include bandwidth requests;
the RS can group the bandwidth requests and then send one bandwidth-request MAC
PDU to BS as an aggregation bandwidth request for all received requests. RS also

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can group MAC PDUs with same latency requirement (QoS), and then it can decide
when to send the grouped PDUs. Since an RS can also combine all the received MAC
PDUs without considering their types, this step is optional.
(iii) The RS combines the MAC PDUs within same category, and then adds its MAC
header and CRC into the combined MAC PDU. One combination method is firstly
removing CRC sequences in the received MAC PDUs, and then linking the individual
MAC PDUs, as shown in Fig. 8. Another method is using a new MAC PDU to replace
the grouped MAC PDUs, as illustrated in Fig. 9. For example, in an OFDMA wireless
system, RS may use one bandwidth request to apply for bandwidth for a group of
devices. Another method is firstly extracting the payload from the received MAC
PDUs, and then combining these payloads in a new MAC PDU, as depicted in Fig. 10.
In this case, the new MAC header should describe how to combine the payloads. In all
above methods, if necessary, a previously configured CID, identifying the connection
between RS and BS, and other information will be added into the new MAC PDU.
(iv) Finally, the RS delivers the MAC PDU to PHY layer to add PHY header and other
information, and transmit this MAC PDU.
2. Operations in BS
Referring to Fig. 11, the following operations take place on the BS side after the
BS receives the new packet having the combined MAC PDU from the RS:
(i) BS checks the CRC (if available) for the received packet from RS. BS will
discard the packets with CRC error;
(ii) BS checks the CID (if available) for the received packet from RS. BS will discard
the packet with unknown CID;

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(iii) BS decodes the MAC PDU, or fragments the linked MAC PDUs if present (Fig. 8)
and decodes them.
Although the above description concerns the processing in a single RS and BS,
other RSs may be present in the network. In this case, in relation to each other RS, the
first RS may act like the BS in the above explanation. Each other RS will serve its own
set of SSs and combine the packets received from those SSs in the same manner as
explained above for the first RS.
An embodiment of the present invention may provide the following effects:
- Defines a protocol for an RS to process the received packets.
- Minimises the PHY overhead by classifying and combining received packets in RS.
- Decreases the collision probability for the contention style packets between RS and
BS.
Embodiments of the present invention may be implemented in hardware, or as
software modules running on one or more processors, or on a combination thereof.
That is, those skilled in the art will appreciate that a microprocessor or digital signal
processor (DSP) may be used in practice to implement some or all of the functionality
of the RS or BS in the present invention. It is also possible to provide each SS with
some or all of the functionality of the RS. The invention may also be embodied as one
or more device or apparatus programs (e.g. computer programs and computer program
products) for carrying out part or all of any of the methods described herein. Such
programs embodying the present invention may be stored on computer-readable
media, or could, for example, be in the form of one or more signals. Such signals may
be data signals downloadable from an Internet website, or provided on a carrier signal,
or in any other form.

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CLAIMS
1. A wireless communication method in a system in which subscriber stations are
each operable for communication with a base station, the base station being capable of
performing simultaneous communications with a plurality of the subscriber stations
simultaneously by exchange of packets each conforming with a layered protocol of said
system, the packets comprising a first portion for defining physical layer (PHY)
parameters and a second portion for defining media access layer (MAC) parameters,
and communications between the subscriber stations and the base station being
performed wholly or partly through at least one relay station, the method comprising
steps of, in the relay station:
receiving a plurality of packets from the subscriber stations;
detecting the second portion of each of the packets;
combining the detected second portions to form a second portion of at least one
new packet; and
transmitting the new packet to the base station.
2. The method according to claim 1, wherein the second portion of each packet
includes error-checking information, and said detecting step comprises checking the
error-checking information of packets received from the subscriber stations and
discarding any packets thereby found to have been incorrectly received.
3. The method according to claim 2, wherein the combining step comprises
removing the error-checking information from the second portion of each received
packet and linking the remainder of each second portion to form the second portion of
the new packet.

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4. The method according to claim 1 or 2, wherein the combining step comprises
forming the new packet with a new second portion representing the aggregate contents
of the second portions of the received packets.
5. The method according to claim 1 or 2, wherein the combining step comprises
extracting a payload, if any, from the second portion of each of the received packets
and combining the payloads so extracted in a new second portion of the new packet.
6. The method according to any preceding claim, further comprising, in the relay
station, categorising the detected second portions of the received packets, and in said
combining step forming a new packet for each category.
7. The method according to claim 6, wherein the categorising step is performed
based on type or service level information contained in each second portion of the
received packets.
8. The method according to claim 7 wherein the type information includes a
designation of the packet as a bandwidth request from a subscriber station to the base
station.
9. The method according to claim 7, wherein received packets having the same
service level information are categorised together for forming a new packet.
10. The method according to claim 9 wherein the transmitting step includes
transmitting each new packet to the base station in order of priority based on the
service level information.

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11. The method according to any preceding claim, wherein the first portion is a PHY
header and the second portion is a MAC protocol data unit (PDU) including a MAC
header.
12. The method according to claim 11, wherein the combining step comprises
providing the new packet with a MAC header identifying the relay station.
13. The method according to claim 11 or 12, wherein said combining step comprises
forming the MAC PDU of the new packet and delivering the same to a PHY layer of the
relay station to add the PHY header.
14. The method according to claim 12 or 13, wherein the base station performs
communications by monitoring active connections with subscriber stations and the
relay station, each such connection having a connection ID, and the relay station
includes the connection ID of its connection with the base station within the MAC
header of the new packet.
15. The method according to any preceding claim, further comprising, in the base
station, receiving the or each new packet sent from the relay station and decoding the
second portion thereof.
16. The method according to claim 15 when dependent on claim 2, further
comprising, in the base station, checking the error-checking information of the or each
new packet sent from the relay station, and discarding any packet found to have been
incorrectly received.

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17. The method according to claim 14, further comprising, in the base station,
checking the connection IDs of received packets and discarding any packet having an
unknown connection ID.
18. The method according to any of claims 15 to 17 when dependent on claim 3,
wherein said decoding step in the base station comprises fragmenting the linked
second portions contained in the new packet sent from the relay station.
19. The method according to any preceding claim, wherein the system comprises a
further relay station arranged for communication with said relay station, the further
relay station performing the same steps as said relay station in relation to further
subscriber stations, the receiving step in said relay station including receiving one or
more packets from said further relay station.
20. The method according to any preceding claim wherein at least some of the
subscriber stations are mobile stations.
21. A wireless communication system in which subscriber stations are each operable
for communication with a base station, the base station being capable of performing
simultaneous communications with a plurality of the subscriber stations simultaneously
by exchange of packets each conforming with a layered protocol of said system, the
packets comprising a first portion for defining physical layer (PHY) parameters and a
second portion for defining media access layer (MAC) parameters, and
communications between the subscriber stations and the base station being performed
wholly or partly through at least one relay station, wherein the relay station comprises:
means for receiving a plurality of packets from the subscriber stations;
means for detecting the second portion of each of the packets;

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means for combining the detected second portions to form a second portion of at
least one new packet; and
means for transmitting the new packet to the base station.
22. A relay station for use in a wireless communication method in a system in which
subscriber stations are each operable for communication with a base station, the base
station being capable of performing simultaneous communications with a plurality of
the subscriber stations simultaneously by exchange of packets each conforming with a
layered protocol of said system, the packets comprising a first portion for defining
physical layer (PHY) parameters and a second portion for defining media access layer
(MAC) parameters, and communications between the subscriber stations and the base
station being performed wholly or partly through the relay station, the relay station
comprising:
means for receiving a plurality of packets from the subscriber stations;
means for detecting the second portion of each of the packets;
means for combining the detected second portions to form a second portion of at
least one new packet; and
means for transmitting the new packet to the base station.
23. The relay station according to claim 22, wherein the second portion of each
packet includes error-checking information, and said detecting means comprises
means for checking the error-checking information of packets received from the
subscriber stations and discarding any packets thereby found to have been incorrectly
received.
24. The relay station according to claim 22, wherein the combining means is
operable for removing the error-checking information from the second portion of each

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received packet and linking the remainder of each second portion to form the second
portion of the new packet.
25. The relay station according to claim 22 or 23, wherein the combining means is
operable for forming the new packet with a new second portion representing the
aggregate contents of the second portions of the received packets.
26. The relay station according to claim 22 or 23, wherein the combining means is
arranged to extract a payload, if any, from the second portion of each of the received
packets and to combine the payloads so extracted in a new second portion of the new
packet.
27. The relay station according to any of claims 22 to 26, further comprising means
for categorising the detected second portions of the received packets, said combining
means forming a new packet for each category.
28. The relay station according to claim 27, wherein the categorising means is
responsive to type or service level information contained in each second portion of the
received packets.
29. The relay station according to claim 28, wherein the type information includes a
designation of the packet as a bandwidth request from a subscriber station to the base
station.
30. The relay station according to claim 28, wherein received packets having the
same service level information are categorised together for forming a new packet.

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31. The relay station according to claim 31 wherein the transmitting step includes
transmitting each new packet to the base station in order of priority based on the
service level information.
32. The relay station according to any of claims 22 to 30, wherein the first portion of
each packet is a PHY header and the second portion is a MAC protocol data unit
(PDU) including a MAC header.
33. The relay station according to claim 32, wherein the combining means is
arranged to provide the new packet with a MAC header identifying the relay station.
34. The relay station according to claim 33, wherein the base station performs
communications by monitoring active connections with the subscriber station and the
relay station, each such connection having a connection ID, and the combining means
is arranged to include the connection ID of its connection with the base station within
the MAC header of the new packet.
35. A computer-readable recording medium storing a computer program which, when
executed by a relay station of a wireless communication system, provides the relay
station according to any of claims 22 to 34.
36. A base station for use in a wireless communication method in a system in which
subscriber stations are each operable for communication with the base station, the
base station being capable of performing simultaneous communications with a plurality
of the subscriber stations simultaneously by exchange of packets each conforming with
a layered protocol of said system, the packets comprising a first portion for defining
physical layer (PHY) parameters and a second portion for defining media access layer

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(MAC) parameters, and communications between the subscriber stations and the base
station being performed wholly or partly through at least one relay station which
receives a plurality of packets from the subscriber stations, detects the second portion
of each of the packets, combines the detected second portions to form a second
portion of at least one new packet, and transmits the new packet to the base station;
wherein the base station comprises:
means for receiving the or each new packet sent from the relay station; and
means for decoding the second portion of the new packet.
37. The base station according to claim 36, wherein the second portion of each
packet includes error-checking information, and said decoding means includes means
for checking the error-checking information of the or each new packet sent from the
relay station, and discarding any packet found to have been incorrectly received.
38. The base station according to claim 36 or 37, wherein the second portion of
every packet contains a connection ID identifying an active connection in the system,
and the base station includes monitoring means which monitors connection IDs of its
own active connections.
39. The base station according to claim 38, wherein said decoding means includes
means for checking the connection IDs of received packets and discarding any packet
having an unknown connection ID.
40. The base station according to any of claims 36 to 39, wherein the new packet
sent from the relay station includes linked second portions of the packets received from
the plurality of subscriber station, and the decoding means comprises means for
fragmenting said linked second portions.

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41. A computer-readable recording medium storing a computer program which, when
executed by a base station of a wireless communication system, provides the base
station according to any of claims 36 to 40.
42. A packet format for use by the relay station in the wireless communication
method according to any of claims 1 to 20, the packet format comprising:
a PHY header for defining physical layer (PHY) parameters of the wireless
communication system; and
a media access layer (MAC) protocol data unit (PDU) for defining media access
layer parameters of the system and including at least a MAC header with optional
payload and error correction code; wherein
in said packet format, the MAC PDU combines individual MAC PDUs of packets
received by the relay station from a plurality of subscriber stations including the MAC
header and any payload thereof but omitting any error correction code thereof.

A wireless communication method in a system, for example a WiMAX system, in which
subscriber stations (MS) are each operable for communication with a base station
(BS), the base station being capable of performing simultaneous communications with
a plurality of the subscriber stations simultaneously by exchange of packets each
conforming with a layered protocol of said system. The packets have a PHY header for
defining physical layer parameters and a MAC PDU for defining media access layer
parameters. Communications between the subscriber stations and the base station
are performed via at least one relay station (RS1#), which receives a plurality of
packets from the subscriber stations (MS) and detects the MAC PDU of each of the
packets. The relay station then combines the detected MAC PDUs to form a MAC
PDU of at least one new packet and transmits the new packet to the base station (BS).
In this way, bandwidth on the uplink from the relay station to the base station is
conserved.