Patent Publication Number: US-2009220085-A1

Title: Relay MAC Header for Tunneling in a Wireless Multi-User Multi-Hop Relay Networks

Description:
RELATED APPLICATION 
     This Application claims priority from U.S. Patent Application Ser. No. 60/970,558, “Encryption and Bandwidth Request and Fragment Sequence Number in Relay MAC Headers” filed by Tao et al. on Sep. 7, 2007, and incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to wireless multi-user relay networks, and more particularly to a MAC protocol header in wireless multi-user, multi-hop relay (MMR) networks. 
     BACKGROUND OF THE INVENTION 
     Orthogonal frequency-division multiplexing (OFDM) is a modulation technique used at the physical layer (PHY) of a number of wireless networks, e.g., networks designed according to the IEEE 802.11a/g standards, and the IEEE 802.16/16e standards. 
     OFDMA is a multiple access scheme based on OFDM. In OFDMA, separate sets of orthogonal tones (subchannels) and time slots are allocated to multiple transceivers of mobile stations (MS) or Users so that the transceivers can communicate concurrently. As an example, the IEEE 802.16/16e standard, has adopted OFDMA as the multiple channel access mechanism for non-line-of-sight (NLOS) communications at frequencies below II GHz. 
       FIG. 1A  shows a conventional OFDMA-based cellular network  100 , e.g., a wireless network according to the IEEE 802.16/16e standard. The network has a point-to-multipoint topology, wherein only two types of network entity exist, namely base stations (BS), and mobile stations (MS). The BS manages and coordinates all communications with the MS in a particular cell on wireless connections  101 - 103 . Each MS is in direct communication with only one BS, and only the BS communicates with an infrastructure  110  or “backbone” of the network. That is, there is only one hop between the MS and the BS. All communications between the MS must pass through the BS. Furthermore, there is only one connection between the BS and each MS. 
     Due to significant loss of signal strength along the connection for certain spectrum, the coverage area of the wireless service is often of limited geographical size. In addition, blocking and random fading frequently results in areas of poor reception, or even dead spots in the cell. Conventionally, this problem has been partially addressed by increasing the number of BS. However, the high cost of the BS and potential increase in interference, among others, render this approach less desirable. 
     As shown in  FIG. 1B  for an alternative approach, a relay-based network  150  can be used. The network includes multiple mobile stations (MS) and/or subscriber stations (SS). A relatively low-cost relay station (RS) extends the range of the BS. Some of the stations (MS 1  and SS 1 ) in close proximity to the BS communicate directly with the BS using connections C 1  and C 2 . Other remote stations (MS 2 , MS 3  and SS 2 ) communicate directly with the RS using connections C 3 , C 4  and C 5 , and indirectly with the BS via corresponding relay links  151  using two hops. Obviously, communications on the relay links  151  between the RS and BS can become a bottleneck. 
     As shown in  FIG. 2  and in order to effectively address this issue on relay link, the mechanism of aggregation and tunneling is described in United States Patent Application 20080107061, “Communicating packets in a wireless multi-user multi-hop relay networks,” filed by Tao et al. on May 8, 2008. With the introduction of aggregation tunnel  210  in the multi-hop relay network, a wide range of new protocol functions are needed to supported the relay links. The tunnel  210  aggregates the multiple links  151  of  FIG. 1B  into a single connection and transmits all the traffic between the BS and the RS as a single bit stream. Thus, instead of having to allocate resources to each of the connections  151 , a single resource can be allocated to the tunnel  210 . 
     As a result, enhancements to the relay medium access control (MAC) header are described in U.S. patent application Ser. No. 11/770,327, “Protocol Data Units and Header in Multi-hop Relay Network,” file by Tao et al. on Jun. 28, 2007. 
     SUMMARY OF THE INVENTION 
     The embodiments of the invention provide a data structure for a relay medium access control (MAC) header communicated in a mobile multi-hop relay network between stations. The header includes a grant management subheader bit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic of a prior art wireless mobile networks; 
         FIG. 1B  is a schematic of a prior art wireless mobile relay network; 
         FIG. 2  is a schematic of a wireless mobile relay network according to embodiments of the invention; 
         FIG. 3  is block diagram of a format of a prior art relay medium access control (MAC) protocol data unit (PDU); 
         FIG. 4  is a block diagram of a format of a prior art relay medium access control (MAC) header; and 
         FIG. 5  is a block diagram of a relay medium access control (MAC) header according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Definitions 
     For the sake of clarify and the description of the invention the following terms are defined and used accordingly herein. 
     Base Station (BS) 
     Equipment to provide wireless communication between subscriber equipment and an infrastructure or network backbone. 
     Subscriber Station (SS) 
     A generalized equipment set to provide communication between the subscriber equipment and the base station (BS). 
     Mobile Station (MS) 
     A wireless transceiver intended to be used while in motion or at unspecified locations. The MS is always a subscriber station (SS) unless specifically specified otherwise. 
     Relay Station (RS) 
     A wireless transceiver whose function is to relay data and control information between other stations, and to execute processes that support multi-hop communications. 
     Connection 
     At a physical layer, a wireless connection runs from an RF transmitter of a station via one or more transmit antennas through a wireless channel to an RF receiver of another station via one or more receive antennas. Physically, the connection communicates RF signals using a predetermined set of subchannels and time slots. 
     At a logical layer, the portion of interest of the connection runs from a media access control (MAC) layer of a protocol stack in the transmitter to the MAC layer in the receiver. Logically, the connection caries data and control information as a single bit stream. For the purpose of this description the connection between the RS and the BS is called a relay link. 
     MAC Service Data Unit (MSDU) 
     A set of data specified in a protocol of a given layer and including of protocol control information of that layer, and possibly user data of that layer. 
     MAC Protocol Data Unit (MPDU) 
     A protocol data unit of a given layer of a protocol including the service data unit coming from a higher layer and the protocol control information of that layer. A burst is a sequence of contiguous MPDUs that belong to the same connection transmitted as a single, uninterrupted bit stream. The embodiments of the invention use relay MPDUs. 
       FIG. 3  shows a format for a relay MAC PDU. The relay MAC PDUs transmitted via the tunnel  210  on the relay link is constructed according to this format. Specifically, the relay MAC PDU includes a relay MAC header  310 , which is followed by optional extended subheaders  320 , a payload  330 , and an optional cyclical redundancy check (CRC)  340 . The payload can include zero or more subheaders  351  and zero or more MAC PDUs  352 . For management purposes, the payload  330  can be a management message type  361  and a management message  362 . 
       FIG. 4  shows a format for a six byte-long relay MAC header. The number in parenthesis indicates the bit assignment in each byte. Specifically, the header type (HT) bit  401  is set to 0 to indicate that the payload is a MPDU. Six bits are reserved (RSV)  402 . The relay mode indication (RMI) bit  403  indicates whether this is a relay MPDU or not. 
     The extended subheader field (ESF)  404  indicates whether there is any extended subheader included in this relay MAC PDU. The 11-bit length field  405  indicates the length in bytes of the entire relay MAC PDU including the (relay) MAC header, and the CRC (if present). The length field is followed by the 16-bit connection identification (CID) field  406 . An 8-bit HCS (header checksum)  407  is appended at the end of the relay MAC header for integrity protection purpose. 
     To support a variety of new functions on the relay link  210 , the reserved bits  402  are used as shown in  FIG. 5 . Specifically, the header includes an encryption control (EC) bit  501 , an allocation subheader (ASH) bit  502 , grant management subheader (GMSH) bit  503 , fragmentation subheader (FSH) bit  504 , a packing subheader (PSH) bit  505 , and a quality of service (QoS) subheader (QSH) bit  506 . 
     There also is a CI bit  507  and an EKS filed 508 described below. Note the length field  405  is now 12 bits to accommodate larger MPDUs for the tunnel. 
     All the novel bits and fields are described below. 
     Encryption Control (EC) Bit 
     If the CID in the relay MAC header indicates that the tunnel  210  is used, then the EC bit  501  indicates whether the payload  330  is encrypted or not. 
     Allocation Subheader (ASH) Bit 
     The ASH bit  502  indicates whether an allocation subheader is present or not. The allocation subheader to instruct the RS when to relay the MAC PDU. 
     Grant Management Subheader (GMSH) Bit 
     The GMSH bit  503  indicates whether a grant management subheader is present or not in an uplink relay MAC PDU. The grant management subheader is way to attach a request uplink bandwidth without having to create and transmit a complete MPDU with the overhead of MAC headers and CRCs. 
     Fragmentation Subheader (FSH) Bit 
     The FSH bit  504  indicates whether a fragmentation subheader is present or not. 
     Packing Subheader (PSH) Bit 
     The PSH bit  505  indicates whether a packing subheader is present or not. 
     Quality of Service (QoS) Subheader (QSH) Bit 
     The QSH bit indicates whether a QoS subheader is present or not. 
     CRC Indication (CI) Bit 
     The CI bit  507  indicates whether the CRC  340  is present or not. 
     Encryption Key Sequence (EKS) Field 
     The EKS field  508  indicates the use of an encryption key sequence. 
     Length Field 
     This field indicates a total length in bytes of the relay MPDU, including the relay MAC header and the optional CRC field (if present). In order to support a larger payload, the length field in the relay MAC header is 12-bit long. Note that the length field in the conventional IEEE 802.16 generic MAC header (GMH) is 1 I-bit long. 
     The format for the header of the relay MAC PDU shown in  FIG. 5  is further described in Table 1. 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Syntax 
                 Size 
                 Notes 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Relay MAC 
                   
               
               
                 Header( ) { 
               
            
           
           
               
               
               
               
               
            
               
                   
                 HT 
                 1 
                 bit 
                 0 
               
               
                   
                 EC 
                 1 
                 bit 
                 Encryption control, if CID in the relay MAC 
               
            
           
           
               
               
               
            
               
                   
                   
                 header is a transport tunnel CID 
               
               
                   
                   
                 = 0: payload is not encrypted 
               
               
                   
                   
                 = 1: payload is encrypted 
               
            
           
           
               
               
               
               
               
            
               
                   
                 RMI 
                 1 
                 bit 
                 Relay mode indication = 1 
               
               
                   
                 ASH 
                 1 
                 bit 
                 Allocation subheader 
               
            
           
           
               
               
               
            
               
                   
                   
                 = 0: allocation subheader is absent 
               
               
                   
                   
                 = 1: allocation subheader is present 
               
            
           
           
               
               
               
               
               
            
               
                   
                 GMSH 
                 1 
                 bit 
                 Grant management subheader (GMSH) in 
               
            
           
           
               
               
               
            
               
                   
                   
                 uplink 
               
               
                   
                   
                 = 0: GMSH is absent 
               
               
                   
                   
                 = 1 : GMSH is present 
               
            
           
           
               
               
               
               
               
            
               
                   
                 FSH 
                 1 
                 bit 
                 Fragmentation subheader (FSH) 
               
            
           
           
               
               
               
            
               
                   
                   
                 = 0: FSH is absent 
               
               
                   
                   
                 = 1: FSH is present 
               
            
           
           
               
               
               
               
               
            
               
                   
                 PSH 
                 1 
                 bit 
                 Packing subheader (PSH) 
               
            
           
           
               
               
               
            
               
                   
                   
                 = 0: PSH is absent 
               
               
                   
                   
                 = 1: PSH is present 
               
            
           
           
               
               
               
               
               
            
               
                   
                 QSH 
                 1 
                 bit 
                 QoS subheader (QSH) 
               
            
           
           
               
               
               
            
               
                   
                   
                 = 0: QSH is absent 
               
               
                   
                   
                 = 1: QSH is present 
               
            
           
           
               
               
               
               
               
            
               
                   
                 ESF 
                 1 
                 bit 
                 Extended subheader field. 
               
            
           
           
               
               
               
            
               
                   
                   
                 = 0: the extended subheader is absent. 
               
               
                   
                   
                 = 1: the extended subheader is present and 
               
               
                   
                   
                 will follow the GMH immediately. 
               
               
                   
                   
                 The ESF is applicable both in the DL and in 
               
               
                   
                   
                 the UL. 
               
            
           
           
               
               
               
               
               
            
               
                   
                 CI 
                 1 
                 bit 
                 CRC indicator 
               
            
           
           
               
               
               
            
               
                   
                   
                 = 0: no CRC is included 
               
               
                   
                   
                 = 1: CRC is included in the relay MAC PDU 
               
            
           
           
               
               
               
               
               
            
               
                   
                 EKS 
                 2 
                 bits 
                 Encryption key sequence. 
               
            
           
           
               
               
               
            
               
                   
                   
                 This field contains the index of the traffic 
               
               
                   
                   
                 encryption key (TEK) of the access RS 
               
               
                   
                   
                 operating in distributed security mode and 
               
               
                   
                   
                 initialization vector (IV) used to encrypt the 
               
               
                   
                   
                 payload. 
               
            
           
           
               
               
               
               
            
               
                   
                 LEN 
                 12 
                 bits 
               
            
           
           
               
               
               
               
               
            
               
                   
                 CID 
                 16 
                 bits 
                 tunnel CID 
               
               
                   
                 HCS 
                 8 
                 bits 
                 Header check sequence 
               
            
           
           
               
               
            
               
                 } 
               
               
                   
               
            
           
         
       
     
     It is to be understood that various other adaptations and modifications can be made within the spirit and scope of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.