Wireless communication systems

This application claims foreign priority benefits under 35 U.S.C. §119 of United Kingdom Application No. GB 0620370.7, filed on Oct. 13, 2006, entitled “Wireless Communication Systems”.

This invention relates in general to wireless communication systems, and more particularly to processing bandwidth requests in a wireless communication system.

Overview

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 (also called “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).

The media access layer is responsible for handling network access, bandwidth allocation, and maintaining connections. 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. A connection between a base station and subscriber station (more precisely, between MAC layers in those devices—so-called peer entities) is assigned a connection ID (CID) and the base station keeps track of CIDs for managing its active connections. 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 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 FIG. 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):

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 bandwidth requests among 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, FIG. 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). FIG. 4 shows a generic MAC header format as specified in IEEE 802.16-2004, including a 16-bit CID.

In single hop systems as envisaged in IEEE 802.16, each subscriber station (SS) will request bandwidth directly from the base station (BS), thus sharing the access to a common base station. If the SS has not got any bandwidth, in the network entry and initialization stage, it will use a CDMA ranging code to request bandwidth. The BS handles these requests on a contention basis as already mentioned. Once the SS gets some initial bandwidth, it may subsequently use a stand-alone bandwidth request MAC (Media Access Control) header or Piggyback request to further request bandwidth. The Piggyback bandwidth request shall always be incremental. The stand-alone request can be incremental or aggregate.

The service flow between SS and BS can be created and activated during network entry procedure or by dynamic service flow procedure. 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 shall never be associated with more than one transport ID, and a transport CID shall never be associated with more than one SFID. The CID will be enclosed with the bandwidth request, thus the BS can know which SS requests bandwidth, and what is the associated QoS demand.

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. FIG. 5 shows an example of such a configuration having two relay stations labeled RS 1 # and RS 2 #. If the network is modified to support relaying functionality as shown in FIG. 5 , normally, the relay station (RS) will relay the band requests (BRs) of all SSs or RSs within its coverage to the BS.

The problem with this bandwidth request protocol is that BS will face many bandwidth request messages, which means a lot of bandwidth between BS and RS 1 #, and contention is likely to be needed between these bandwidth requests. Especially, when the number of hops is more than two, the number of bandwidth requests between BS and its closest RS, such as RS 1 # in FIG. 5 , will be accumulated, thus more bandwidth will be used for signaling overhead. This is a particular problem since in general, uplink bandwidth is more constrained than downlink bandwidth. Moreover, when a CDMA ranging code is used for bandwidth request, the increased number of bandwidth requests received by the BS will increase the collision probability of the transmission of the broadcasted CDMA codes.

On the other hand, in non-transparent or distributed relay systems, an RS may deal with the burst dimensioning, bandwidth allocation, and packet scheduling by itself. These operations are also relevant to bandwidth allocation for the radio devices within its cell. Therefore, it is possible for an RS to be involved in the bandwidth request procedure.

In accordance with one embodiment of the present invention, a wireless communication method in a wireless communication system is provided. In the wireless communication system, subscriber stations are each operable to communicate with a base station and the base station is capable of performing simultaneous communications with a number of subscriber stations by allocating an available capacity among the subscriber stations. The subscriber stations are required to issue capacity requests in order to obtain and/or maintain a connection with the base station, and communications between the subscriber stations and the base station are performed partly or wholly through at least one relay station. The provided wireless communication method includes, in the relay station, detecting capacity requests issued from a plurality of the subscriber stations, using the detected requests to form at least one combined capacity request, and transmitting the combined capacity request to the base station. Furthermore, the method includes, in the base station, responding to the combined capacity request by reserving capacity for said plurality of subscriber stations. In addition, the method includes, in the relay station or in the base station, allocating the reserved capacity among the plurality of subscriber stations.

For a more complete understanding of the present invention and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows protocol layering in accordance with IEEE 802.16;

FIG. 2 shows the relationship between CID, SFID and QoS in an IEEE 802.16 network;

FIG. 3 shows a packet format capable of being used in an IEEE 802.16 network;

FIG. 4 shows a generic MAC header of a packet as set forth in the IEEE 802.16 specification;

FIG. 5 illustrates a simple bandwidth request protocol in a multi-hop wireless communication system;

FIG. 6 illustrates the bandwidth request (BR) protocol employed in particular embodiments of the present invention;

FIG. 7 is a flowchart of processing of initial bandwidth requests in a relay station (RS);

FIG. 8 is a flowchart of processing of further bandwidth requests in the RS;

FIG. 9 shows a first message format of a combined instant BR in accordance with particular embodiments of the present invention; and

FIG. 10 shows a second message format of a combined instant BR in accordance with particular embodiments of the present invention.

An embodiment of the present invention will now be described with reference to FIGS. 6-10 , using an IEEE 802.16 network as an example. An algorithm is proposed by which the relay station can classify and combine the bandwidth requests from the subscriber stations (or any other relay station) within its cell, and submit the combined bandwidth requests to the base station, thus decreasing the overhead and collision of bandwidth request messages. This is schematically shown in FIG. 6 , in which the subscriber stations are mobile stations denoted by MS. The thick arrow in FIG. 6 represents a combined BR formed in the RS and replacing the multiple parallel BRs relayed by the RS in FIG. 5 . As already mentioned, bandwidth requests (BRs) fall into two categories, initial BRs and further BRs, and these are treated differently in the present embodiment.

1. Initial Bandwidth Request

In the network entry and initialization stage, each SS within range of an RS will use contention-based CDMA ranging for requesting initial bandwidth. When the RS detects these CDMA codes, it can send a different CDMA code to the BS to request bandwidth for these SSs, rather than simply relaying two detected CDMA codes to BS, thus saving bandwidth and decreasing the collision probability of the CDMA code transmission surround BS. Alternatively, the RS can use a stand-alone bandwidth request MAC header to request bandwidth for these SSs. This procedure is shown in the flowchart of FIG. 7 .

2. Further Bandwidth Request

As explained above, once the SS gets some initial bandwidth, it may subsequently use a stand-alone bandwidth request MAC (Media Access Control) header or Piggyback request to further request bandwidth. In this stage, the RS classifies the received standalone or Piggyback BRs into “Instant BR” (IBR), and “Non-instant BR” (NIBR). The IBRs will be combined and sent to BS by RS as soon as possible. The NIBRs will be combined and sent by periodical aggregate BR by RS. The procedure in the relay station for processing such further BRs is shown in FIG. 8 . The first stage is for the RS to receive BRs. Then RS shall identify the QoS parameters relating to the service flow of the corresponding bandwidth request. For example, an RS can index the connection ID (CID) enclosed within the BRs to find the QoS demands. To allow RS to learn the QoS demands of service flows, during the service connection request period, BS has to tell the RS the information of the approved service flows. Alternatively, an RS can “listen in” to the information exchanged during the service connection request period to obtain the QoS associated with the CID, and the relationship between service flow and CID.

In light of QoS demands, the received BRs will be classified into two categories, IBR, and NIBR, by RS. For example, the BRs relevant to Unsolicited Grant Service (UGC), and Real-time Polling Service (rtPS) may be identified as IBR. The BRs for Best Effort (BE), and Non-real-time Polling Service (nrtPS) may be classified as NIBR.

If the number of received IBRs is one, then RS records the amount of the bandwidth requested by this IBR, and simply sends this IBR to BS as soon as possible. This IBR can be incremental or aggregate. The RS will keep the original CID for this IBR. If the number of received IBRs in the current frame is more than one, then RS will combine these IBRs to one BR, called combined IBR, and send this combined BR to BS as soon as possible. In this case, the RS will also record the aggregation of the requested bandwidth of all IBRs. This combined BR can be incremental or aggregate.

A first possible message format of a combined IBR is shown in FIG. 9 (Format A). The details of this control message format are listed in Table 1 below.

To decrease the size of the control message of a combined IBR, the RS can use the message format shown in FIG. 10 (Format B). The details of this control message are listed in Table 2. When using this message format, the RS will use one of its existing (previously configured) CIDs, which is associated with all CIDs used by its SS, or MS, and RS. The BS will know that the bandwidth request enclosed with this CID is used for the SSs and any other RSs connected to the RS.

After processing the IBRs, the RS will record the aggregation of the requested bandwidth by all NIBRs. When the timer for periodical RS bandwidth request is expired, the RS will work out the aggregation of the bandwidth needed for its uplink transmission, and transmit an aggregate bandwidth request to the BS. The RS can use the “message format B” in FIG. 10 for this bandwidth request. Therefore, an existing CID is needed by RS to associate all CIDs connected to itself. The period of the aggregate bandwidth request may be a function of the QoS of the services relating to NIBRs, and of the link quality.

In response to the BR from the RS, the BS performs necessary processing for allocation of bandwidth. In the case of a format A bandwidth request ( FIG. 9 ), the amounts of bandwidth (incremental or aggregate) required by the individual SSs (or other RSs) is contained in the request from the RS. In this case the BS must allocate bandwidth on an individual basis and notify the RS accordingly, the RS then simply noting the amounts so notified. In the case of a format B bandwidth request ( FIG. 10 ), the BS grants the requested amount (if possible; otherwise a lesser amount) and informs the RS accordingly. It is then up to the RS to allocate the granted bandwidth by dividing up the granted amount appropriately among the requesting SSs/RSs, in dependence upon their QoS requirements.

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 BRs received from those SSs in the same manner as explained above for the first RS.

In summary, certain embodiments of the present invention may provide one or more of the following features:

Defining a protocol for an RS to process the received bandwidth requests. Minimizing the control message overhead by classifying and combining received bandwidth requests in RS. Decreasing the collision probability for the contention style bandwidth request. The method proposed can be used for other message relaying, thus achieving the above benefits.

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 particular embodiments of the present invention. It is also possible to provide each SS with some or all of the functionality of the RS. Particular embodiments of 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.

Although the present invention has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alterations, transformations, and modifications as fall within the scope of the appended claims.