RELAY SELECTION AND CONNECTIVITY IN MOBILE MULTIHOP RELAY NETWORK NURUL NAZIRAH BINTI MOHD IMAM MA' AROF A thesis submitted in fulfilment of the requirements for the award of the degree of Doctor of Philosophy (Electrical Engineering) Faculty of Electrical Engineering Universiti Teknologi Malaysia MAY 2016
v ABSTRACT Mobile Multihop Relay (MMR) network is an attractive and low-cost solution for expanding service coverage and enhancing throughput of the conventional single hop network. However, mobility of Mobile Station (MS) in MMR network might lead to performance degradation in terms of Quality of Service (QoS). Selecting an appropriate Relay Station (RS) that can support data transmission for high mobility MS to enhance QoS is one of the challenges in MMR network. The main goal of the work is to develop and enhance relay selection mechanisms that can assure continuous connectivity while ensuring QoS in MMR network. The first approach is to develop and enhance a relay selection for MS with continuous connectivity in non-transparent relay. In this approach, the standard network entry procedure is modified to allow continuous connectivity with reduced signalling messages whenever MS joins RS that is out of Multihop Relay Base Station (MRBS) coverage and the relay selection is based on Signal to Noise Ratio (SNR). The second approach is to develop and enhance relay selection that allows cooperative data transmission in transparent relay that guarantees continuous connectivity. The proposed relay selection defined as Cooperative Relay Selection based on SNR and LET (Co-ReSL) depends on weightage of SNR, a and weightage of Link Expiration Time (LET), B. National Chiao Tung University network simulator (NCTUns) is used in the simulation study. The QoS performances of the proposed relay selections are in terms of throughput and average end-to-end (ETE) delay. The findings for the proposed relay selection in non-transparent relay shows that at heavy traffic load p=0.8, and MS speed of 30 mis, throughput increases by 2.0% and average ETE delay reduces by 9.0% compared to random relay selection due to selection of RS with good link quality and provision of continuous connectivity. In addition, the throughput degradation between low mobility MS (30 mls) and high mobility MS (50 mls) is only about 2.0%. Findings for Co-ReSL show that at heavy traffic load, throughput increases up to 5.7% and average ETE delay reduces by 7.5% compared to Movement Aware Greedy Forwarding (MAGF) due to cooperative data transmission in selective links. By setting a=0.8 for Co-ReSL, the decrement of throughput between low mobility MS and high mobility MS is about 2.3% compared to the rapid decrement of 5.5% and 6.0% experienced by Co-ReSL with a=o.2 and MAGF, respectively. In addition, Co-ReSL improves throughput by 11.9% and reduces average ETE delay by 7.7% compared to non-cooperative method. The proposed relay selection mechanisms can be applied in any high mobility multitier cellular network.
vi ABSTRAK Rangkaian Pengulang Banyak-Iompatan Bergerak (MMR) adalah penyelesaian menarik dan rendah kos untuk memperluaskan liputan perkhidmatan dan meningkatkan kadar penghantaran data rangkaian tanpa wayar lompatan tunggal konvensional. Walau bagaimanapun, mobiliti Stesen Bergerak (MS) dalam rangkaian MMR mungkin menyebabkan penurunan prestasi dari segi Kualiti Perkhidmatan (QoS). Salah satu cabaran dalam rangkaian MMR adalah pemilihan Stesen Pengulang (RS) yang sesuai yang boleh menyokong penghantaran data untuk mobiliti MS yang tinggi bagi meningkatkan QoS. Matlamat utama kerja ini adalah untuk membangunkan mekanisme pemilihan pengulang yang boleh memberi jaminan sambungan berterusan di samping memastikan QoS dalam rangkaian MMR. Pendekatan pertama adalah untuk membangunkan satu mekanisme pemilihan pengulang untuk MS dengan sambungan berterusan dalam pengulang tidak telus. Dalam pendekatan ini, prosedur kemasukan rangkaian standard diubah suai untuk membenarkan sambungan berterusan dengan mengurangkan isyarat mesej bila-bila masa MS menyertai RS yang berada di luar liputan Stesen Pangkalan Pengulang Banyak-Iompatan (MRBS). Pemilihan pengulang adalah berdasarkan kepada Nisbah Isyarat kepada Gangguan (SNR). Pendekatan kedua adalah untuk membangunkan pemilihan pengulang yang membolehkan penghantaran data secara kerjasama dalam pengulang telus yang menjamin sambungan berterusan. Pemilihan pengulang yang dicadangkan didefinisikan sebagai Pemilihan Relay secara Kerjasama berdasarkan SNR dan LET (Co-ReSL) bergantung kepada pemberatan SNR, a dan pemberatan Masa Sambungan Tamat (LET),. Simulasi rangkaian Universiti Kebangsaan Chiao Tung (NCTUns) digunakan dalam kajian simulasi. Prestasi QoS bagi pemilihan pengulang yang dicadangkan adalah kadar celus dan purata kelewatan hujung-kehujung (ETE). Hasil kajian pemilihan pengulang yang dicadangkan dalam pengulang tidak telus menunjukkan bahawa pada beban trafik p=0.8 dan kelajuan MS 30 mis, kadar celus meningkat sebanyak 2.0% dan purata kelewatan ETE berkurang sebanyak 9.0% berbanding dengan pemilihan RS dengan kualiti pautan yang baik dan peruntukan sambungan berterusan. Tambahan pula, kemerosotan kadar celus antara mobiliti MS rendah (30 mls) dan mobility MS tinggi (50 mls) hanya kira-kira 2.0%. Hasil kajian Co-ReSL menunjukkan bahawa pada beban trafik berat, kadar celus meningkat sehingga 5.7% dan purata kelewatan ETE berkurang sebanyak 7.5% berbanding dengan Pemajuan Tamak Peka Gerakan (MAGF) disebabkan oleh penghantaran data secara kerjasama dalam pautan terpilih. Dengan menetapkan a=0.8 untuk Co-ReSL, kadar celus antara mobiliti rendah MS dan mobiliti tinggi MS susut kira-kira 2.3% berbanding dengan susutan yang cepat sebanyak 5.5% dan 6.0% yang dialami oleh Co-ReSL dengan a=o.2 dan MAGF, masing-masing. Co-ReSL meningkatkan kadar celus sebanyak 11.9% dan mengurangkan purata kelewatan ETE sebanyak 7.7% berbanding dengan kaedah tidak kerjasama, Mekanisme pemilihan pengulang yang dicadangkan boleh digunakan dalam mana-mana rangkaian selular pelbagai peringkat yang bermobiliti tinggi.
vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION 11 DEDICATION 111 ACKNOWLEDGEMENT ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS LIST OF SYMBOLS LIST OF APPENDIX IV v VI vii Xl XlI xv xviii xxii 1 INTRODUCTION 1 1.1 Background 1 1.2 Problem Statement 2 1.3 Objectives of the Research 4 1.4 Scope of the Research 4 1.5 Research Contributions 5 1.6 Significance of the Research 6 1.7 Thesis Organization 6 2 LITERATURE REVIEW 8 2.1 Introduction 8 2.2 Mobile Multihop Relay Networks 9 2.2.1 Relay-assisted in MMR Networks 11
viii 2.2.2 Features ofmmr Networks 16 2.2.3 RS Operation Mode 18 2.2.4 Network Entry Procedure in MMR Network 19 2.2.5 Type ofrs 23 2.2.6 Cooperative Transmission 23 2.3 Related Works 24 2.3.1 Relay Selection in MMR Network 25 2.3.1 Relay Selection Strategy 25 2.3.2 Existing Relay Selection Scheme 26 2.3.2 Cooperative Transmission III MMR Network 33 2.4 Research Motivation 35 3 DESIGN APPROACH FOR RELAY SELECTION MECHANISMS IN MOBILE MULTIHOP RELAY NETWORKS 38 3.1 Introduction 38 3.2 Relay Selection Framework in MMR Networks 39 3.2.1 Proposed Relay Selection III Nontransparent Relay Mode 42 3.2.2 Proposed Cooperative Relay Selection in Transparent Relay Mode 45 3.3 Link Feature 3.3.1 Signal to Noise Ratio 3.3.2 Link Expiration Time 3.4 Network Simulation Model 3.4.1 Non-transparent Relay Mode 3.4.2 Transparent Relay Mode 3.5 NCTUns System Description 3.6 Simulation Tools 3.7 Performance Measure 3.8 Summary 48 48 50 52 53 55 61 64 65 67
ix 4 RELAY SELECTION FOR NON-TRANSPARENT RELAY MODE IN MOBILE MULTIHOP NETWORKS 68 4.1 Introduction 68 4.2 Relay Selection for MMR Networks 68 4.2.1 Proposed Connectivity Procedure 69 4.2.2 Relay Selection Mechanism 76 4.3 Analytical and Simulation Study of MMR Network Model 80 4.3.1 Validation ofmmr Network Model 82 4.4 Simulation Study of Relay Selection 85 4.4.1 Effect of Stationary and Moving MS 85 4.4.2 Effect of Traffic Load 88 4.4.3 Effect of Mobility 90 4.5 Summary 93 5 COOPERATIVE RELAY SELECTION FOR TRANSPARENT RELAY MODE IN MOBILE MULTIHOP RELAY NETWORKS 5.1 Introduction 5.2 Cooperative Relay 5.2.1 Weight Score 5.2.2 Relay Selection Scheme 5.3 Simulation Result Selection for MMR Networks 94 94 94 95 103 108 5.3.1 Selection for weight of SNR factor, a and weight of LET factor, B 109 5.3.2 Effect of Traffic Load 111 5.3.3 Effect of Mobility 114 5.3.4 Effect of Cooperative Relay Transmission 117 5.4 Summary 119
x 6 CONCLUSION AND FUTURE WORKS 6.1 Introduction 6.2 Significant Achievements 6.3 Future Works 121 121 121 124 REFERENCES 127 Appendices A - B 135-204
xi LIST OF TABLES TABLE NO. TITLE PAGE 2.1 Different traffic classes and QoS requirement [39] 11 2.2 Summary of existing relay selection scheme 32 2.3 Summary of existing cooperative transmission 35 3.1 Adaptive and Modulation Coding (AMC) schemes [77] 50 3.2 Parameter setting for non-transparent relay mode 55 3.3 Parameter setting for transparent relay mode 60 5.1 Determination of packet received at the MRBS 106
xii LIST OF FIGURES FIGURE NO. TITLE PAGE 2.1 A simple MMR network architecture [34] 10 2.2 Scenario for fixed, nomadic and mobile RS [10] 12 2.3 Multihop relaying in mobile network [47] 13 2.4 Handover scenarios in conventional cellular networks 16 2.5 Types of communication links in MMR network 17 2.6 RS operation mode (a) Transparent relay mode (b) Nontransparent relay mode 19 2.7 Comparison of network entry procedure between (a) transparent, (b) non-transparent relay modes [71] 21 2.8 Simple cooperation 3.1 General process of the relay communication 24 selection mechanisms 40 3.2 Scenario for the relay selection (a) Non-transparent relay mode (b) Transparent relay mode 41 3.3 Design framework for relay selection in non-transparent relay mode 43 3.4 CLD approach for relay selection in non-transparent relay mode 44 3.5 Design framework for Co-ReSL in transparent relay mode 45 3.6 CLD approach for Co-ReSL in transparent relay mode 46 3.7 Exemplary of the relationship between SNR and distance 49 3.8 Exemplary of the relationship between LET and distance 52 3.9 (a) MSl (far from RSl) (b) MS2 (near to RSl) (c) Moving MS3 moves toward RS2 53 3.10 Network simulation topology for non-transparent relay
X111 3.11 3.12 3.13 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 5.1 5.2 5.3 5.4 mode Network simulation topology for transparent relay mode AMC region in IEEE 802.16j network systems [116] Path decision based on weightage condition Limitation scenario in non-transparent relay mode Network topology for the proposed connectivity procedure Modified network entry procedure Modified network entry state machine on the MS side Difference network topology (a) Fully covered by RS (b) Partially covered by RS Flow chart for relay selection based on SNR A simple network topology to validate with queuing model MID/I queue model Average total time in the system Average waiting time in the queue Average number of packets in the system Average number of packets in the queue Packet loss rate comparison Throughput comparison Average ETE delay comparison for fixed and MS for fixed and MS for fixed and MS Packet loss rate for different traffic load (speed = 30 m/s) = Throughput for different traffic load (speed 30 m/s) Average ETE delay for different traffic load (MS speed 30 m/s) Packet loss rate for different MS speed (p 0.8) = Throughput for different MS speed (p = 0.8) Average ETE delay for different MS speed (p 0.8) = Modulation and coding rate under various SNR Exemplary scenario for LET validation The mobile station movement traces Flow chart for Co-ReSL = 54 56 57 61 71 73 74 75 77 79 80 81 83 83 84 84 87 87 88 89 89 90 91 92 92 97 100 103 104
xiv 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 Link availability during MS movement at different time. Decision of next hop relay station Packet loss rate in different weight of SNR factor, a Throughput in different weight of SNR factor, a Average ETE delay in different weight of SNR factor, a Packet loss rate among MAGF and Co-ReSL (MS speed=3 Omls) Throughput among MAGF and Co-ReSL (MS speed=30mls) Average ETE delay among MAGF and Co-ReSL (MS speed=30mls) Packet loss rate for different MS speed (p = 0.8) Throughput for different MS speed (p = 0.8) Average ETE delay for different MS speed (p Packet loss rate for different number of relays Throughput for different number of relays Average ETE delay for different number of relays = 0.8) 105 108 110 110 111 112 113 113 115 116 116 118 118 119
xv LIST OF ABBREVIATIONS AF AMC AN AODV API ARP BE BS BWA CBR CDMA CID CLD CM Co-ReSL CR DCD DF DL DL-MAP DT-FWD ertps ETE FIFO FRS FTP Amplify-and-Forward Adaptive Modulation and Coding Active Node Ad-hoc On-demand Distance Vector Application Programming Interface Address Resolution Protocol Best Effort Base Station Broadband Wireless Access Constant Bit Rate Code Division Multiple Access Connection Identification Cross Layer Design Channel Model Cooperative Relay Cognitive Radio Downlink Channel Descriptor Decode-and- Forward Downlink Downlink map Data Forwarding extended real-time Polling Service End to End First In First Out Fixed RS File Transfer Protocol Selection based on SNR and LET
xvi GPS GUI HTTP IMT IP IR ITS LAN LET LOS LTE MAC MAGF MANET MCN MCS MMR MRBS MRS MS MSID NLOS NRS nrtps PHY PKM-REQ PKM-RSP QAM QoS QPSK REG-RSP REP-SYNC REQ-SYNC Global Positioning System Graphical user interface Hypertext Transfer Protocol International Mobile Telecommunications Internet Protocol Initial Ranging Intelligent Transport System Local Area Network Link Expiration Time Line of Sight Long Term Evaluation Medium Access Control Movement Aware Greedy Forwarding Mobile Ad-hoc Network Multihop Cellular Network Modulation and Coding Scheme Mobile Multihop Relay Multihop Relay Base Station Mobile Relay Station Mobile Station Mobile Station Identity Non Line of Sight Nomadic RS non-real-time Polling Service Physical Privacy Key Management Request Privacy Key Management Response Quadrature amplitude modulation Quality of Service Quadrature Phase Shift Keying Registration Response Reply Synchronization Request Synchronization
xvii ReSL RNG-REQ RNG-RSP RS rtps SBC-REQ SBC-RSP SNR SS SSH STA-ACK STA-INFO TCP/IP UCD UDP/IP UGS UL UL-MAP VoIP WiMAX WSN Relay Selection based on SNR and LET Ranging Request Ranging Response Relay Station real time Polling Service Subscriber station basic capability request Subscriber station basic capability respond Signal to Noise Ratio Subscriber Station Secure Shell Station Acknowledgement station information Transmission Control Protocoll Internet Protocol Uplink Channel Descriptor User Datagram Protocol/Internet Protocol Unsolicited Grant Service Uplink Uplink map Voice over Internet Protocol Worldwide Interoperability Wireless Sensor Network of Microwave Access
xviii LIST OF SYMBOLS Maximum transmission range o Instantaneous received SNR SNR threshold N Number of transmission modes supported by MMR network r Transmission range Speed of node i Coordinates of node i Movement direction angels for node i Relative velocity of the receiver node with respect to the sender node along Y-axis b Distance of the receiver node from the sender node c along X-axis Relative velocity of receiver node with respect sender node along Y-axis to the d Distance of the receiver node from the sender node along Y-axis f1 II. Service rate Arrival rate Received SNR from MS to the RS (fame. NOFDMA SNR threshold from AMC table Weight ofbs-ms Weight ofms-rs Weight ofrs-bs Number of OFDMA symbols per slots Number of subcarriers per slot
' xix CR Coding rate Modulated symbol Frame duration Packet loss rate Total number of packet transmitted from the source node Total number or packets received at the destination node DelaYETE time rx, timetx, Np T Average end-to-end delay Time packet Time packet i received at the destination node i transmit from the source node Total number of packets being transmitted Throughput Time needed for the last packet N arnve at the destination node t, Time for the time required for the first packet i send from the source node Lq P L wt; wt Wi a fj LETs LETD Ii, t İ. (Xi'.v., dist, ) Average number of packets in the queue Traffic load of the node Average number of packets in the system Average waiting time in the queue Average waiting time in the system Weighted score Weight of SNR Weight of LET Supply LET LET demanded by the network Current locations of node i Nodes i's locations after t time units Nodes i's coordinate after t time units Distance of nodes i and b based speed on node i moving
xx Nodes i's velocity after t time units Start time I t Time after moving MSi RSi RSUst Clist Plist CurrentMS Neighbor RS List of RSi List of candidate RSi List of potential RSi Sorted potential RSi Received power Transmit power Antenna gain at receiver Antenna gain at transmitter Path loss SNR value between MSiand RSiLink Noise figure Thermal noise level Effective channel bandwidth Frequency sampling Number of data subscriber Nppr LETi Nexthop In pjr SRi FFT size LET value between MSiand RSiLink Selected next hop to forward data packets Number of potential RSs Minimum transmit power of source-p, Minimum transmit power of Ri-destination Corresponding channels of source-to-re1ay link Corresponding channels of relay Interference from source to destination to destination link Interference from R, to destination Interference threshold of base station
xxi Optimal relay Number of cooperative relaying Pm rtable Data packet Routing table
xxii LIST OF APPENDIX APPENDIX TITLE PAGE A B List of Publications Source Code 135 137
CHAPTER 1 INTRODUCTION 1.1 Background Rapid growth in number of mobile connected devices such as smart phones and tablets leads to the demand for high capacity network with high data rate and QoS provisioning for multimedia applications. In order to meet these requirements, next-generation cellular network needs to extend network capacity and coverage. Under limited frequency resources, the conventional approach to enhance network capacity is by installing more MRBS to exploit spatial reuse. However, this is not an efficient solution because the cost to install MRBS is high. An alternative approach to reduce the cost is to employ low cost RS in assisting data transmission between MRBS and MS in MMR network [1], [2]. MMR has emerged as a potential technology for data transmission in cellular mobile network. MMR network can provide high data rate and thus capacity enhancement, coverage extension and mobility support. It is low cost network deployment and provides QoS improvement for multiple types of applications [3], [4]. In MMR network, multihop RS is introduced to assist data transmission between MRBS and MS when single hop link quality is not good. The concept of MMR network is similar to traditional Multihop Cellular Network (MCN). In this network, MS with good link quality can directly communicate with MRBS while MS with poor link quality, especially the ones
2 located at the cell edges, communicates with MRBS via RS. RSs provide multiple links to be used for data transmission from MS to MRBS and vice versa. Efficient relay selection techniques are required to determine reliable links among the available links based on system parameters such as link quality[5], [6], traffic load [7] and radio resource availability [8]. As mentioned earlier, MSs located at cell edges receives very low signal strength from MRBS, which lead to higher probability of link failures. Moreover, node mobility is an additional factor that causes link failure to occur frequently in the network. Link failure between nodes degrade network performance severely [9]. Multihop relaying is a renowned technique that supports frequent change of network topology [10]. Hence, exploiting multihop relaying technology and equip it with awareness towards varying link stability due to node mobility is essential in order to enhance network performance [11]. In mobile communication, MS may suffer from performance degradation due to the time varying channel condition. This leads to limitation of the data rate and network QoS. Cooperative transmission may enhance network performance by using multiple RSs in assisting data transmission between MRBS and MS. Whenever a link is broken due to bad link condition or node mobility, other RSs that provide better connection to the MS can be chosen. Thus, the average end-to-end (ETE) delay and throughput can be improved. Cooperative communication has been considered as an efficient solution in multihop relaying [12]-[14] because it provides higher throughput, robustness for time varying channel [15], [16], space diversity gain, and enable users to transmit data at high speed and with high reliability. 1.2 Problem Statement The main issue for MS in MMR network is performance degradation due to node mobility. When MS moves, it needs to change network or roams from the current RS to another RS. Additional delay is introduced each time MS intends to
3 attach to another RS which causes the average ETE delay to increase. If the coverage range of RS is large, the duration of nodes staying connected is high, so the frequency to change network is reduced and vice versa. However, in practical, coverage range of RS is not as large as MRBS coverage due to its smaller transmission power. Therefore, there is a need for a mechanism to choose an appropriate RS effectively whenever MS moves out of current network coverage to maintain continuous connectivity and hence high throughput for the MS [17], [18]. It is clearly understood in the literature that multihop relaying extends network coverage area and enhances network capacity [19], [20], [21]. However, as MS moves from one point to another point, the performance is degraded due to random variation of channel and network condition [22], [23]. Therefore, proper selection of RS to overcome the performance degradation problem during data transmission is one of the challenging tasks in MMR network. Usage ofrs provides multiple communication links between MRBS and MS. Each communication link may have different characteristics. Due to the path loss and shadowing experienced for each communication link [7], [8], [24], link quality, channel condition, traffic load and radio resource availability are affected. Therefore, there is a need to select the potential communication link that meets QoS requirements. The demand for multimedia service with higher data rate leads to requirement of high network capacity in next generation cellular network. Traditional approach to overcome network capacity requirement by installing more MRBS to support QoS guarantee for multiple types of applications [3], [4] is costly for MRBS installation is expensive, thus, RS is used since it offers a cost effective solution with lower complexity. However, the usage of RSs incurs higher delay and may degrade multimedia throughput due to multihopping transmission. Thus, there must be a proper relay links usage that can minimize delay and enhance throughput.
4 1.3 Objectives of the Research The main goal of this work is to develop relay selection mechanisms to enhance mobility support and QoS performance of MS in MMR network. Two types of RS operation modes have been considered in this work namely non-transparent and transparent relay modes. The specific objectives of the thesis include: i) To develop and enhance relay selection mechanism with continuous connectivity for MSs in non-transparent MMR network. ii) To develop and enhance relay selection that ensures continuous connectivity in transparent MMR network through cooperative data transmissions. The QoS performance metrics considered in this work are throughput and average ETE delay of MSs in the MMR network. Relay selection mechanisms in both transparent and non-transparent relay network will be dealt separately to overcome the different issues encountered in each network. 1.4 Scope of the Research In this work the MMR network is assumed to operate up to two hops. The MSs are assumed moving and the changing speed may vary up to SOmis (180 km/h). The proposed relay selection mechanisms with continuous connectivity to enhance QoS performance in MMR network have been developed for transparent and nontransparent relay mode. The work can be divided into three main focus issues: i) In the non-transparent mode the coverage range is enhanced through continuous connectivity for MSs in MMR network. As the MS moves outside the coverage range of current RS, it can continue to be connected to other RS through the proposed connectivity procedure directly linked to the relay without incurring the repetition of the network procedure.
- The 5 ii) Second, effective relay selection mechanism is developed for MS in MMR network. Additionally, link quality information is used to choose the suitable modulation type and coding rate based on Modulation and Coding (MCS) scheme for data transmission. Implementation of the modulation type and coding rate with the highest number of bits per symbol is expected to increase the data rate, and thus enhance throughput in MMR network. iii) Finally, cooperative and relay selection mechanism is developed enhance the network performance in terms of throughput and delay. to further In this work, NCTUns simulation tool is used to measure the network performance in MMR network because NCTUns supports the IEEE 802.16j standardization. 1.5 Research Contributions The proposed relay selection mechanism enhances QoS performance of MSs in MMR network through continuous connectivity, relay selection mechanism and cooperative relay transmission. The significance contributions achieved from this research work are as follows: i) Support of continuous connectivity for MS in non-transparent relay mode - During data transmission MS is allowed to move out of MRBS coverage range and yet continues to be connected to the network through other relay stations through a connectivity procedure without having to perform lengthy network entry procedures. The proposed connectivity procedure reduces signalling overhead. ii) Relay selection mechanisms that decide based on link quality stability and link relay selections have significantly enhanced MS throughput and minimizes MS ETE delay of high mobility MSs in MMR network.