Multihop cellular networks (MCNs) have drawn tremendous attention due to its high throughput and extensive coverage. However, there are still three issues not well addressed. With the existence of relay stations (RSs), how to efficiently allocate frequency resource to relay links becomes a challenging design issue. For mobile stations (MSs) near the cell edge, cochannel interference (CCI) become severe, which significantly affects the network performance. Furthermore, the unbalanced user distribution will result in traffic congestion and inability to guarantee quality of service (QoS). To address these problems, we propose a quantitative study on adaptive resource allocation schemes by jointly considering interference coordination (IC) and load balancing (LB) in MCNs. In this paper, we focus on the downlink of OFDMA-based MCNs with time division duplex (TDD) mode, and analyze the characteristics of resource allocation according to IEEE 802.16j/m specification. We also design a novel frequency reuse scheme to mitigate interference and maintain high spectral efficiency, and provide practical LB-based handover mechanisms which can evenly distribute the traffic and guarantee users' QoS. Our study shows that our scheme not only meets the requirement on coverage, but also improves the throughput while accommodating more users in MCNs.

By incorporating relay technologies into cellular systems, multi-hop relay networks (MRNs) can provide higher throughput and wider coverage, but it is impossible to guarantee quality of service (QoS) requirements for users at the cell edge and in hot spots due to severe co-channel interference (CCI) and load imbalance. This paper proposes an adaptive resource allocation scheme with a joint consideration of interference coordination (IC) & load balancing (LB), and analyzes the downlink of orthogonal frequency division multiple access (OFDMA) based MRNs with time division duplex (TDD) mode. We present a novel frequency reuse scheme for MRNs to mitigate CCI and maintain high spectral efficiency. We also provide practical LB-based handover mechanisms to evenly distribute users and guarantee the users' QoS. Extensive simulations demonstrate that our scheme not only satisfies the requirement of coverage probability, but also improves the throughput and accommodates more users in MRNs.

The multi-hop cellular network (MCN) is an evolved paradigm for mobile communications, which integrates the ad hoc characteristics into the conventional cellular systems. Similar to ad hoc networks, the performance of MCNs relies on the hypothesis that each node accepts to forward traffic for the benefit of others, which may not hold with the possible presence of selfish users. In order to stimulate the collaboration among mobile nodes in MCNs, in this paper, we propose a light-weighted secure incentive protocol (LIP). We introduce a novel reward model, in which not the source and/or the destination but the network operator credits the forwarding nodes. It is shown that our model is much more realistic for MCNs in practice and simplifies the payment scheme design as well. LIP exploits a reactive receipt-submission mechanism to identify node behavior, which significantly reduces the communication overhead. Security analysis shows that LIP can resist various attacks. The efficiency of LIP is validated through the performance evaluation.

When many cellular users take high capacity transit (HCT), a group of mobile terminals (MTs) may have to initiate handoffs and location updates more or less at the same time, which will cause congestion on the random access control channel (RACH), leading to many handoff and location update failures. To overcome this problem, we propose a new scheme, called GHA/RALU (Group Handoff Avoidance/Rate Adjusted Location Update Scheme), to deal with this group mobility issue. The idea is first to delay the normal location update (NLU) requests until the group handoff requests are completed and then spread the NLU requests within a calculated time interval based on the available bandwidth of the RACH. Our analysis shows that the proposed scheme significantly improves the success probability of the group handoffs and NLUs, saves the RACH resource, and accelerates the handoff initiated by the moving-in-together MTs.

Wireless Relay networks have become very important technologies in the future wireless systems. Current research works mostly focus on scenarios where relay stations are either stationary or mobile with uniform velocity. However, in many applications, relay stations are mobile with irregular patterns. In particular, when mobile relay stations (MRSs) are deployed to complement the cellular systems, many issues such as handoff should be carefully investigated. In this paper, we focus on the handoff problem and propose a new handoff decision algorithm based on the relative velocities of user equipment (UE) to the serving access point (AP) and the target AP. We have show that the proposed handoff algorithm can significantly improve the handoff successful rate when the mobile relay station changes its moving patterns.

As all-IP feature becomes dominant in the next generation networks (NGNs), ad hoc mode is gaining more attention as an appealing addition to cellular networks. Consequently, multi-hop handoffs become inevitable, which bring challenging issues to network designers. Handoff dropping (HOD) rate and the bandwidth reservation for the required HOD rate are two important metrics to evaluate the handoff performance of a cellular system. By introducing ad hoc mode into cellular systems, we can either achieve lower HOD rate or reserve less bandwidth for the same required HOD rate. In this paper, we incorporate traffic information from neighboring BSs and propose an algorithm to find the minimum bandwidth reservation for each BS. Since its performance greatly depends on the access probability to the adjacent cells, we further propose to utilize the embedded ad hoc networks to gather the traffic load information of neighboring cells. With such information, handoff calls can effectively select the best paths to the proper BSs. It has been demonstrated that our scheme can significantly improve the system performance.

Spectrum sharing is a crucial issue to the overall throughput performance of multi-hop wireless networks. Traditional distributed random medium access control (MAC), such as IEEE 802.11, lacks of efficiency of spectrum usage, while centralized scheduling is not practical for large scale ad hoc networks. It is observed that for multi-hop wireless networks, it is hard to resolve the scheduling conflict, and most distributed algorithms consider the neighbors' traffic independent of each other and ignore the multi-hop nature of flows, leading to the spectrum wastage and inefficiency. By incorporating the multihop nature of flows, we propose a new distributed scheme based on IEEE 802.11 standard, namely "2-hop MAC". Nodes collect traffic dependency information as well as traffic demand information from neighbors and allocate spectrum distributedly with the knowledge of more accurate traffic demand of the nodes in the neighborhood. Moreover, we have also addressed the problem of the asymmetric neighborhood, which was ignored in most previous work. Finally, we introduce a new metric, namely, allocation inefficiency ratio (AIR), to evaluate the performance of distributed algorithms in multi-hop wireless networks. Extensive simulation study shows that our proposed scheme can significantly improve the network performance and spectrum efficiency.

Recent studies indicate that by improving the spatial reuse ratio the throughput of 802.11 wireless networks can be improved. In this paper, we study the impact of physical carrier sensing and channel rate on the throughput of 802.11 wireless networks with chain topology. Firstly, this paper propose

Current deployment of the wireless mesh networks (WMN) necessitates mobility management to support mobile clients roaming around the network without service interruption. Though Mobile IP and other previous protocols can be applied to WMNs to gain the micro-mobility as well as macro-mobility support, high signaling cost and long handoff latency problems still degrade the system performance significantly. In this paper we present a new mobility management scheme for WMNs, mesh mobility management (M3). It utilizes some WMN's features and combines the per-host routing and tunneling techniques to reduce the signaling cost as well as to shorten the handoff latency. Our analysis shows that significant benefits can be achieved from this scheme.

Using multi-channel MAC protocols in mobile ad hoc networks (MANETs) is a promising way to improve the through-put performance. Channel assignment, which directly determines the efficiency of the frequency utilization, is the critical part of multi-channel schemes. Current 802.11-like schemes of multi-channel MAC do not efficiently use the multiple channels due to the overhead caused by channel assignment. Moreover, the control channel saturation problem limits the number of channels of these previous schemes. In this paper, we propose a new scheme called SAM-MAC (Self-Adjustable Multi-channel MAC), which features with one common channel and two half-duplex transceivers for each node. A method called self-adjustment is used to reassign the channels and balance the traffic on different channels. Due to less contention in common channel and smaller channel assignment overhead, this scheme increases the throughput compared with previous approaches. Control channels are free from saturation problem and can furthermore be used for data transmission.