Multi-hop wireless mesh networks (M-WMNs) have recently emerged as an alternative network infrastructure. For M-WMNs to serve as a network infrastructure, the protocol designs for M-WMNs should target a high network capacity. An efficient backoff algorithm is required to achieve a high network capacity. Most of existing works focused on backoff algorithms for infrastructure environment based on IEEE 802.11 distributed coordination function (DCF) or did not consider the features of M-WMN. In this paper, we propose an adaptive backoff algorithm based on the number of contention nodes for an IEEE 802.11 DCF-based M-WMN. The proposed backoff algorithm is founded on cross-layer cooperation between the routing and the medium access control (MAC) layers. The number of contention nodes of a node is obtained from the routing layer, and then this information is used to adaptively adjust the value of the minimum contention window (CWmin) in the backoff mechanism of the MAC protocol. To evaluate the performance of the proposed backoff algorithm and existing ones, computer simulations were performed. The simulation results show that the existing algorithms do not work well in M-WMN and the proposed backoff algorithm outperforms existing ones.

In this paper, we give an analytical justification how to control the QoS parameters using a throughput approximation model for IEEE 802.11e EDCA. Using the model, we propose a new parameter control algorithm which successfully achieves the dynamic parameter assignment under desired throughput ratio constraints.

Wireless mesh networks (WMNs) are one of the key features of beyond 3G system because of their flexible and low-cost deployment. IEEE 802.16 mesh mode has recently emerged as an alternative protocol for establishing WMN. Because the WMN is used as wireless backbone network, the design of WMN protocol should target a high network throughput. Then, in IEEE 802.16 mesh standard, the performance improvement is limited by the holdoff algorithm in the bandwidth reservation procedure. In this paper, we propose an adaptive holdoff algorithm for IEEE 802.16 mesh mode with coordinated distributed scheduling. The proposed holdoff algorithm improves network throughput by adaptively adjusting the transmission holdoff exponent according to current node state. In addition, the proposed holdoff algorithm maintains the backward compatibility with the IEEE 802.16 mesh standard and does not require any information from other layers. Simulation results show that the proposed holdoff algorithm performs better than existing holdoff algorithm in terms of total network throughput.

In spite of using IEEE 802.11 as medium access control (MAC), most of the ad-hoc routing protocols do not consider contention time that occurs in the medium reservation procedure. Large, contention times can be more critical than hop counts in determining the end-to-end delay. In ad-hoc networks, traffic concentration on some mobile nodes leads to long queuing delays, low packet delivery ratios, and inefficient power consumption. In this paper, we propose an ad-hoc routing protocol with minimum contention time and load balancing (MCL). MCL has two main characteristics. Firstly, MCL selects a route with minimum contention among many possible routes between source and destination in the route selection procedure; secondly, intermediate nodes do not reply to RREQs in the route discovery procedure. These characteristics reduce contention time in medium reservation procedure and distribute traffic throughout the network. We have compared the proposed MCL and the ad-hoc on-demand distance vector (AODV) routing protocol. Simulation results show that MCL outperforms AODV in terms of packet delivery ratio, average end-to-end delay, and normalized routing overhead. In situation where several mobile nodes send data to a fixed node such as an access point or a server, our proposed routing protocol MCL delivers a high performance gain as a result of load balancing.

Bluetooth has been regarded as a promising solution for wireless connection between hand-held devices. In Bluetooth, a message is segmented into short packets to be transmitted over different frequency bands to randomize error occurrences. There are various kinds of packets with different sizes and error-handling schemes. Since each packet type has its own performance characteristics, care must be taken in selecting a packet type. This paper proposes an adaptive method that selects the best packet type depending on the condition of the channel. One of challenging issues in the proposed scheme is how to predict the packet error rate of one packet type from another. We interpolate packet error rates of different packets based on a uniform bit error model. Based on the packet error rates obtained from the interpolation, the proposed scheme selects a packet type that leads to the best performance. We also propose a revised scheme that works even when bit errors occur in a non-uniform pattern. The proposed scheme is especially useful in a harsh environment where the bit error rate is worse than 10/sup -4/.