Isameldin Suliman

Queueing analysis of opportunistic access in cognitive radios

This paper presents queueing analysis of opportunistic access in cognitive radios. The primary (licensed user) has priority over the secondary user and it does not need to care about the secondary user transmissions. A time slotted system is assumed, so that the secondary user can perform spectrum sensing at the beginning of the slot to know if it is occupied by primary or not. If the slot is free, it can be utilized for secondary transmissions. This leads to no interference with primary user communication, assuming perfect sensing. Finding waiting time and queue length of this type of system has not, according to our best knowledge, been performed before. We perform theoretical analysis by applying M/D/1 priority queueing scheme. The results were used to evaluate the performance of the cognitive network. Simulation are used to validate the results, and simulation results demonstrate a high degree of accuracy for the derived expressions. Results indicate that the performance of the secondary user depends on the data traffic characteristics of the primary user, and under high arrival rate for the primary, the average waiting and average queueing length of the secondary user grow especially when the combined arrival rate approach the queue utilization factor.

Analysis of cognitive radio networks with imperfect sensing

Recently, cognitive radio access has received much attention. Spectrum sensing methods are often used for finding free channels to be used by cognitive radios (secondary users). State diagram based approach can be used for analyzing the effects of imperfect spectrum sensing (with false alarms and misdetections). The state diagram consists of two-tuples like (1,2) meaning one primary user and two secondary users present. We note that state dependent transition rates are very important for accurate modeling. This is because for example in state (3,0) (all channels occupied by primary users) collisions happen with increased probability. Our contribution is as follows. Explicit expressions for state dependent transition rates are presented for the case with three channels. However, the approach can be used also for more channels. Primary termination probability is used for evaluating the level of interference to primary users caused by secondary users. Secondary success probability is used to find out how often does a secondary call start and terminate successfully. Simulation and analysis results agree very well.

A comparison study between wireless bridging and routing

Routers and bridges are the basic devices used for building data networks. In particular, wireless bridges provide a means to extend network coverage range by wirelessly linking access points. In this paper, we investigate the performance of TCP and UDP protocols using routing and two different bridging configurations. We report measurements made over a heterogenous multihop wireless network. The results show that TCP and UDP protocols perform better with bridging (using two WLAN cards) than with routing. However, when bridging is configured with only one WLAN card, the throughput decreased significantly. Our tests indicate that routing and bridging with two cards are more affected by variation in TCP and UDP packet sizes than bridging with one card. Both TCP and UDP throughput increase with packet size. The best result is achieved when the packet size is 1500.

Preamble sense multiple access (PSMA) for impulse radio ultra wideband sensor networks

In this paper we propose preamble sense multiple access (PSMA), a random access MAC protocol capable of clear channel assessment in impulse radio-ultra wideband environment. Full compatibility with IEEE 802.15.4a contention access period is the key design criteria of PSMA, and the goal is to provide an alternative approach to the 802.15.4a envisioned slotted ALOHA and periodic preamble segment transmission schemes. The evaluation of PSMA consists of a traditional throughput analysis as well as energy consumption and delay analysis that takes into account the special features of impulse radio ultra wideband approach. From the analysis we can claim that PSMA has a very good energy and delay performance in addition to satisfactory throughput when the offered traffic to the channel is from low to moderate.

A cooperative multihop radio resource allocation in next generation networks

With the objectives of improving 3G networks coverage by using relaying nodes, a game theoretic approach to radio resource allocation for the downlink capacity is introduced. One of the basic issues not examined in the literature is the importance of fair resource sharing among mobile nodes located along a multihop link. We describe a novel technique for providing a resource allocation mechanism in a multihop relaying network. The resource allocation problem is formulated as a cooperative game using Nash Bargaining Solution (NBS), which allows mobile nodes to fairly share a downlink bandwidth among themselves. Sharing of the downlink capacity between multiple nodes using a noncooperative approach is inefficient when the radio resource is scarce. If upstream nodes manipulate their location at the head of the multihop link to exploit the downlink capacity, downstream nodes will suffer disproportionately. The undesirable properties can be avoided by means of a cooperative agreement in which all nodes share the radio resources equally, where downstream nodes are allowed to pay compensation to prevent upstream nodes from exploiting the downlink capacity and encourage them to cooperate.

Performance evaluation of videostreaming on a heterogenous multihop mobile network

Recent wireless technologies have enough bandwidth to support even demanding applications such as multimedia transmissions. Quite often, mobile networks have wireless routers using different technologies and characteristics (heterogenous networks). The paper describes our implementation experiences in constructing a multihop heterogenous mobile network using Bluetooth and IEEE 802.11b. We measured packet latency and throughput of the network and subjective video quality when using a videoconferencing application. Videoconferencing over IP (VCoIP) is known to have rather strict bandwidth and latency requirements. Our results indicate that it is possible to use VCoIP, but, depending on the link technologies used, the quality of service can be severely degraded.

Optimizing Detection Parameters for Time-Slotted Cognitive Radios

Recently, cognitive radio access in time-slotted systems has gained interest. In these systems, the beginning of the slot is used for detection. If no signal is found to be present, remainder of the slot can be used for cognitive radios (secondary users). Detection of the occupancy status of the slots is characterized by false alarm probability and detection probability. The detection probability needs to be large enough to protect primary user. However, too large detection probability means increased false alarm probability thus reducing the secondary users transmit opportunities. We study finding the optimum false alarm and detection probabilities. Numerical results indicate that the secondary users maximum throughput is obtained when the random access probabilities are equal to one and random access is handled instead with false alarm probabilities.

Performance measurements of TCP on a heterogeneous wireless multihop network

Future communication networks are expected to be heterogeneous consisting of different wireless systems such as cellular, WLAN, and Bluetooth systems. In this paper we examine the end-to-end performance of TCP protocol over IPv6 on a heterogenous multihop wireless network. We examine how the throughput is affected by using variable TCP window size, variable packet size, and variable datarates. Our results show that there is a certain window size which maximizes the TCP throughput. We found that sending TCP traffic with large packet sizes results in an improved end-to-end throughput. Similar results were obtained when sending TCP traffic at high data rates. The round trip time (RTT) measurements indicate that there is strong correlation between the RTT and window size. The experiments emphasize that with dynamic tuning of TCP window size, large improvements in throughput can be attained. The significance of this work is that it provides results obtained from a real network testbed.