WO2012087109A1

WO2012087109A1 - Scheduling method for multi-hop relay networks

Info

Publication number: WO2012087109A1
Application number: PCT/MY2011/000154
Authority: WO
Inventors: Sabri Mousa Saqer AHMAD; Syamsul Azmir Bin Raja Abdullah RAJA; Ahmad Salah ASEM; Munawar ARIS
Original assignee: Mimos Berhad
Priority date: 2010-12-20
Filing date: 2011-06-23
Publication date: 2012-06-28
Also published as: MY158542A

Abstract

A centralized scheduling method for reducing end-to-end delay in a multi-hop relay wireless network comprising: transmitting bandwidth availability data of the wireless network from a base station to a relay station in between predetermined intervals; and responding a bandwidth request from a mobile station by the relay station immediately using the transmitted bandwidth availability data; wherein the bandwidth request is granted or vice versa by the relay station prior to expiry of the transmitted data.

Description

SCHEDULING METHOD FOR MULTI-HOP RELAY NETWORKS

FTELD OF INVENTION

The present invention relates to a method for reducing the average end-to-end delay in the scheduling of a multi-hop relay network. In more particular, the present invention provides a method for relegating a substantial part of the role for granting bandwidth request to the relay stations (RS) which is performed solely by the multi-hop relay base stations (MR-BS) for a non-transparent centralized scheduling of a multi-hop relay network.

BACKGROUND OF THE INVENTION

IEEE 802.16j Multihop Relay (MR) is developed as an alternative deployment in order to enhance coverage and performance for Worldwide Interoperability for Microwave Access (WiMAX) network by eliminating costly Base Stations (BSs). Other than the multi-hop relay base station (MR-BS), the main elements in a multi- hop relay (MR) network are the relay station (RS) and the mobile station (MS) in which every RS is supervised by a MR-BS while the MS refers to the global system such as mobile phone or mobile computer which are connected to the global network. The MR-BS is called a BS for short hereinafter.

The transmission link that connects between the MS and the BS through the RS in a multi-hop relay (MR) network comprises an access link and a relay link. The access link is a communication link starting from or ending at the MS which is connected to the BS or to the RS. Conversely, the relay link is a link between the BS and the subordinate RS or a communication link between two RSs.

SUBSTITUTE SHEET In a WIMAX multi-hop non-transparent relay network, the relay path and connections setup can be organized in the schemes of centralized and distributed scheduling. These are two scheduling modes which are specified for controlling the allocation resources to the access link and relay link in a multi-hop relay network. In the centralized scheduling mode, the resource allocation for RS's subordinate station is determined at the BS. The BS determine the bandwidth allocation, and generating all the corresponding control channel information including mapping messages (MAPS) for all the access and relay links. The relay network hereinafter refers to a non- transparent centralized scheduling multi-hop relay network.

For non-transparent relays, the RS looks like the base station (BS) to an MS wherein the RS allocates resources for an MS and generates the frame header including the MAP messages. The RS will be a part of the neighbour list scan and a call can be initiated in the RS and handed to the BS.

The standard procedure for the scheduling is initiated by the BS polling for bandwitdth request from the MS after a service flow has been created. At the same time, the BS also allocate bandwidth in an Uplink Map (UL-MAP) message in order to acquire the bandwidth request from the MS during the polling process. The bandwidth can be utilized by the MS to send request information and upon receiving the request information, the BS transmits the requested bandwitdth for data transmission to the MS.

However, the MS may be located in an area where link is more readily to be established with a proximate RS for intermediary facilitation of communication between MS and BS. In a centralized scheduling, the RS is required to send request information to the BS for the decision to allow bandwidth access as requested by the MS. The compulsory routes for the bandwidth request and grant from one terminal to the other end may cause delay in the system delivery which lead to a high signaling overhead. Therefore an invention which could increase the efficiency of the signalling

SUBSTITUTE SHEET scheme by decreasing the end-to-end delay between the mobile station and the base station is highly desirable.

One of the closest inventions over the prior arts is the U.S Patent Application No. 2008/0152031 for reducing delay time by disclosing an uplink scheduling method for the BS in communication system where each MS is allocated a frequency band by the BS to transmit data. Regardless, the invention concentrated in the uplink scheduling and do not take into consideration of the RS which is an important improvement in the wireless communication system to optimize the service coverage area,

SUMMARY OF INVENTION

The primary object of the present invention is to provide a method for a non- transparent centralized multihop relay network's transmission of bandwidths availability data that consists of information for free usable bandwidth subcarrier in a downlink map (DL-MAP) or uplink map (UL-MAP) messages from a BS to the RSs in advance prior to the bandwidth request sent by the MS. Another object of the present invention is to provide a method for non-transparent centralized scheduling to reduce end-to-end delay in the uplink or downlink service flow in the network and thus cutting down on the signaling overhead.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which one of the embodiments of the present invention describes a centralized scheduling method for reducing end-to-end delay in a multi-hop relay wireless network, comprising: transmitting bandwidth availability data of the wireless network from a base station to a relay station in between predetermined intervals; and responding a bandwidth request from a mobile station by the relay station immediately using the transmitted bandwidth availability data; wherein the bandwidth

SUBSTITUTE SHEET request is granted or vice versa by the relay station prior to expiry of the transmitted data.

In a preferred embodiment of the present invention, the centralized scheduling method for reducing end-to-end delay further comprises a step of acquiring updated bandwidth availability data in the latest time interval from the base station to replace the expired data from the previous intervals by the relay station.

In another preferred embodiment of the present invention, the centralized scheduling method further comprises a step of forwarding a corresponding subscription message from the relay station to the base station when the request is granted.

In yet another embodiment of the present invention is a centralized scheduling system for reducing end-to-end delay in a multi-hop relay wireless network, comprising: a base station for transmitting bandwidth availability data at a predetermined time interval; a relay station for receiving the bandwidth availability data from the base station and responding to one or more bandwidth requests from one or more mobile stations; wherein the relay stations grant the bandwidth request or vice versa based on the transmitted bandwidth availability data prior to expiry of the data.

One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which

SUBSTITUTE SHEET when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated. Figure 1 is a schematic diagram describing the scheduling procedure of the prior arts is a schematic diagram describing the scheduling procedure in accordance with one of the preferred embodiment of the present invention

Figure 3 is a flow chart describing the scheme of signaling messages as described as one of the preferred embodiment of the present invention Figure 4 is a bar chart showing the comparison of simulation result of end-to- end delay between the network as described as one of the preferred embodiment of the present invention.

Figure 5 is a graph showing the BS MAC Overhead of the network as described in an embodiment of the present invention in comparison to that of prior arts

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for reducing the average end-to-end delay in the scheduling of a multi-hop relay network. In more particular, the present invention provides a method for relegating a substantial part of the role for granting bandwidth request which is decided solely by the multi-hop relay base stations (BSs) to the relay stations (RSs) for a non-transparent centralized scheduling of a multi-hop relay

SUBSTITUTE SHEET network.

Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim. The present invention discloses a centralized scheduling method for reducing end-to- end delay in a multi-hop relay wireless network comprising a centralized scheduling method for reducing end-to-end delay in a multi-hop relay wireless network comprising: transmitting bandwidth availability data of the wireless network from a base station to a relay station in between predetermined intervals; and responding a bandwidth request from a mobile station by the relay station immediately using the transmitted bandwidth availability data; wherein the bandwidth request is granted or vice versa by the relay station prior to expiry of the transmitted data.

According to the preferred embodiment of the present invention, the method is applicable to the non-transparent centralized scheduling multi-hop relay wireless network in compliance with the IEEE 802.16j standards. Figure 1 shows generally a conventional scheduling procedure for relay station in ΓΕΕΕ 802.16j multihop relay system. Preferably, the request or response signalling can be based on polling scheme which is contention-free or request scheme which is contention-based.

In one of the preferred embodiment of the present invention, the schedule is initiated by the BS which is polling for bandwidth request either directly from the MS with a service flow or through the RS. Bandwidth in UL-MAP message can be allocated by the BS during the polling process for bandwidth request from the MS. By utilizing the bandwidth allocated from the BS to the MS, the MS is able to transmit bandwidth

SUBSTITUTE SHEET request directly to the BS or via RS. Upon receiving of the request, the BS grants a request based on the bandwidth availability data which consists of information on the available bandwidth subcarriers that can be subscribed by the MS. If granted, the RS forwards the corresponding bandwidth subscription message to the BS to inform the central scheduler at the BS to allocate and transmit the amount of bandwidth for data transmission as requested from the MS.

The scheduling procedure with the embodiment of the present invention is shown in Figure 2. In a preferred embodiment, the BS is instructed to forward the data on available bandwidth to the RS before receiving a bandwidth request message from the MS. By providing the proactive step, RS receive information for available bandwidth that can be subscribed by the MS in advance. Thus, the RS is able to grant a request according to the bandwidth availability data. In this way, the bandwidth request message do not need to be transmitted to the BS which leads to the reduction of end- to-end (E2E) delay between the BS and MS.

Now referring to Figure 3, a flow chart describing a non-transparent centralized scheduling process 100 for multi-hop relay wireless network with the embodiment of present invention. The process 100 is provided for easy understanding of the present invention. Besides, the invention is not limited to the order in which the steps are listed in the process 100.

The process 100 is initiated at starting step 101. At starting step (101), the BS transmits bandwidth availability data in downlink or uplink MAP (DIJUL MAP) from time to time to the RS. In an exemplary embodiment, a centralized scheduler with a function of scheduling the service flow by determining the bandwidth subcarriers in specific timeslot is disposed at the base station. The RS may acts as the intermediate transmission for the service flows between the BS and the MS. In addition, the centralized scheduler also transmit control messages including the bandwidth subcarriers.

SUBSTITUTE SHEET In another preferred embodiment, the RS receives the service flows in the form of burst of data packets from the BS. Preferably, the RS have a physical layer to encode and decode the data packets up to a media access control level. Most preferrably, the RS receives updated bandwidth availability data from the centralized scheduler in between time interval in order to replace expired data from the previous intervals. In a further preferred embodiment, the RS sends the data packets to the MS at the subscribed bandwidth subcarriers.

In an exemplary embodiment, the BS transmits bandwidth availability data which consists of usable bandwidth subcarriers in specific timeslots in accordance to the Orthogonal Frequency Division Multiple Access (OFDMA) technology that are available to be subscribed to the MS. The usable bandwidth is divided into a large number of smaller bandwidths that are mathematically orthogonal using fast Fourier transforms (FFTs). Reconstruction of the band is performed by the inverse fast Fourier transform (IFFT). The FFTs and IFFTs are sized as powers of 2.

Preferably, the RS receives the latest updated bandwidth availability data in DL/UL- MAP messages from the BS at bandwidth availability data reception step (102). Preferably, the MS transmits a bandwidth request message by using the bandwidth allocated in an UL-MAP message from the BS back to the BS at bandwidth- requesting step (103).

Preferably, the RS acquires updated bandwidth availability data in the latest time intervals from the BS to replace the expired data from the previous time intervals at bandwidth availability data acquisition step (104).

Preferably, the RS verifies whether a bandwidth availability data in a time interval has expired at data expiry verification step (105).

SUBSTITUTE SHEET Preferably, the RS checks for available bandwidth using the data at bandwidth availability verification step (106). In the event when the data has expired in a time interval, the RS acquires or waits for the updated data from the BS. Preferably, the RS responds to the MS requests according to the bandwidth availability data by indicating the grant status at request-responding step (107). In one of the most preferred embodiment, the RS indicates to the MS by transmitting a DL/UL-MAP messages from its frame. In the event when all of the bandwidth subcarriers are occupied, the RS rejects the request. On the other hand when bandwidths are available, the RS grants the request and forward the corresponding bandwidth subcription request message to the BS so that the BS in response will allocate and transmit the amount of bandwidth requested from the MS.

In an exemplary embodiment, the MS is attached to a network through an RS wherein the connection between the MS and RS is recognized by a BS. After establishing synchronization with the RS, the MS starts a network entry procedure by sending an initial OFDMA ranging code on the uplink ranging channel dedicated for this purpose. When the RS detects from the received code that the MS needs to adjust frequency, timing and/or transmission power, it transmits the message to the BS and the BS sends back an RNG-RSP message to instruct the MS to adjust transmission parameter and send a code again.

In another exemplary embodiment, the MS sends an RNG-REQ message containing MAC address after successful adjustment of transmission parameters. The MS which has not been allocated with any unique connection identifier (CID) uses ranging CID to send the message. The RS relays it to the BS after changing the CED field in the header from the ranging CTD to the RS basic CTD so that the BS can identify which RS directly communicates with the MS. After registering the MS MAC address and its parent RS, the BS assigns MS management CEDs and sends them to the MS using the RNG-RSP message. After management connections assignment, management

SUBSTITUTE SHEET messages are exchanged between the BS and MS via the S which is based on the MS management CEDs.

Figure 4 shows the simulation results comparing the average end-to-end delay between the BS that broadcasts the information on available free bandwidth in advance according to the embodiment of the present invention and the BS that make all the decision on the bandwidth grant by itself. In the experiment, end-to-end delay for 20 MSs are measured and the result revealed that the end-to-end delay for the network with the embodiment of the present invention has been effectively reduced.

Figure 5 shows the comparison of the signal overhead for the uplink media access control (UL-MAC) at the BS between the network with the embodiment of the present invention and the conventional network. The experiment measured 40 MSs in which 20 MSs are directed to send constant bit rate (CBR) while the other 20 for receiving the CBR. The result shows that the network with the embodiment of the present invention is able to reduce signaling overhead as compared to the conventional network. Furthermore, the reduction amount of signaling overhead increases with the number of MSs. According to the embodiment of the present invention, an efficient bandwidth request and response signals scheduling scheme is used in order to reduce the scheduling's end-to-end delay by instructing the multi-hop relay BS to inform the non-transparent RS in forward regarding to the network configurations by using the Downlink Map (DL-MAP) or Uplink Map (UL-MAP) messages. By informing the RS in forward, the function of granting bandwidth request which is previously decided solely by the BS is substantially relegated to the RS. Therefore, end-to-end delay can be reduced by enabling the RS to grant bandwidths request without going through the BS.

The present disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred

SUBSTITUTE SHEET form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.

SUBSTITUTE SHEET

Claims

1. A centralized scheduling method for reducing end-to-end delay in a multi-hop relay wireless network, comprising:

transmitting bandwidth availability data of the wireless network from a base station to a relay station in between predetermined intervals; and

responding a bandwidth request from a mobile station by the relay station immediately using the transmitted bandwidth availability data;

wherein the bandwidth request is granted or vice versa by the relay station prior to expiry of the transmitted data.

2. A method according to claim 1 further comprising a step of acquiring updated bandwidth availability data in the latest time interval from the base station to replace the expired data from the previous intervals by the relay station.

3. A method according to claim 1 further comprising a step of forwarding a corresponding subscription message from the relay station to the base station when the request is granted.

4. A method according to claim 1 wherein the relay station grants a bandwidth request based on the information of usable and available bandwidths contained in the data.

5. A method according to claim 1 wherein the bandwidth availability data are transmitted in an uplink map or downlink map messages depending on the direction of the access or relay links.

6. A method according to claim 1 wherein the method is utilized in non- transparent multi-hop relay stations.

SUBSTITUTE SHEET A method according to claim 1 wherein the channel access method used is an Orthogonal Frequency Division Multiplexing or Orthogonal Frequency Division Multiple Access in compliance with the Worldwide Interoperability Microwave Access.

A centralized scheduling system for reducing end-to-end delay in a multi-hop relay wireless network, comprising:

a base station for transmitting bandwidth availability data at a predetermined time interval;

a relay station for receiving the bandwidth availability data from the base station and responding to one or more bandwidth requests from one or more mobile stations;

wherein the relay stations grant the bandwidth request or vice versa based on the transmitted bandwidth availability data prior to expiry of the data.

SUBSTITUTE SHEET