The term pilot pollution in IS-95 CDMA systems is used to indicate that a large number of equally strong pilot signals is present. Those pilots compete with each other to become the serving one and this causes a very high rotation of pilot leadership at the mobile station. As a consequence, the signaling rate on the traffic channel increases, thus degrading the call quality. We present a method of alleviating the pilot pollution problem by means of repeaters. Simulation studies have been carried out on an actual CDMA network suffering from pilot pollution and the results have been verified by field trials. They indicate that repeaters can effectively improve call quality by altering the spacial distribution of pilot signal strength.

When the joint source-channel (JSC) decoder is used for source coding over noisy channels, the JSC decoder may invent errors even though the received data is not corrupted by the channel noise, if the JSC decoder assumes the channel was noisy. A novel encoder algorithm has been recently proposed to improve the performance of the communications system under this situation. In this letter, we propose another algorithm based on conditional entropy-constrained vector quantizer to further improve the encoder. The algorithm proposed in this letter significantly improves the performance of the communications system when the hypothesized channel bit error rate is high.

In this paper, we propose simple but effective modifications of 802.11 MAC (media access control) to resolve efficiency and fairness issues, in wireless ad-hoc networks [2]. Our proposal, based on the flow concept, incorporated faster end-to-end forwarding by assigning higher priority to a node that has packets to relay than others. After completion of end-to-end transmission, the node will be assigned a lower priority level to yield to other nodes. Simulation results show that the proposed scheme (F-MAC) significantly enhances the throughput of ad-hoc networks, while keeping fair sharing of bandwidth among mobile nodes.

This letter discusses how to enhance the capacity of uplink DS-CDMA networks that support multihop transmission. For this purpose, we derived simple theoretic conditions by which one can choose between singlehop- and multihop transmission. Numerical results show that we can significantly increase the radio network capacity by adopting only a few number of multihop transmissions.

In this Letter, we investigate the correlation rate of a random sequence data set which is collected by RFID (Radio Frequency IDentification) readers in an indoor location. Using a passive RFID tag introduces reading error, which causes a loss of original data. From the question of how sensing errors of RFID readers affect the location prediction algorithm used for context awareness services at home, we analyze the correlation rate of a collected data set with respect to RFID reader-sensing error rate. Through our analysis, we conclude that the prediction accuracy can be better or worse than the one of the original data streams according to the error rate. We suggest that the reader specification has to be satisfied by the error boundary which is found in this work for the tolerant location prediction.

To opportunistically use the licensed band, spectrum sensing has a vital role as the core component in cognitive radio systems. However, the accurate detection of the primary signal is always accompanied by significant overhead, reducing the secondary throughput. In this letter, we suggest remedying this problem by adopting multiple-stage spectrum sensing (MSS) technique. Furthermore, we investigate how our proposed MSS can be incorporated into the collaborative spectrum sensing. Our results are encouraging in that the proposed MSS with collaboration significantly reduces the sensing time compared to the conventional sensing scheme.

In this letter, we consider the uplink packet scheduling for non-real-time data users in a DS-CDMA system. As an effort to jointly optimize throughput and fairness, we formulate a time-span minimization problem incorporating the time-multiplexing of different simultaneous transmission schemes. Based on simple rules, we propose efficient scheduling algorithms and compare them with the optimal solution obtained by linear programming.

In this letter, we focus on detecting a random primary user (PU) network for cognitive radio systems in a cooperative manner by using maximum likelihood (ML) detection. Different from traditional PU network models, the random PU network model in this letter considers the randomness in the PU network topology, and so is better suited for describing the infrastructure-less PU network such as an ad hoc network. Since the joint pdf required for the ML detection is hard to obtain in a closed form, we derive approximate ones from the Gaussian approximation. The performance of the proposed algorithm is comparable to the optimal one.

The mobility control of mobile nodes can be an alternative to the transmitting power adjustment in case that fixed transmitting power is just used in the topology control. Assuming the controllable mobility of nodes, we propose four distributed mobility control algorithms assuring the network connectivity and the capacity improvement. We compare the throughput of each algorithm with the widely accepted capacity scale law considering the energy consumption. The proposed mobility-based topology control algorithms are named according to its operational characteristics; RP (Rendezvous Point), NNT (Nearest Neighbor Tracking), DM (Diffusion Model), and GP (Grid Packing). Through extensive simulations, we show that all the proposed algorithms successfully change a partitioned random network topology into a connected network topology without the power control. Furthermore, the topology reconfigured by the mobility control has the improved network capacity beyond that of the initial network. In the newly defined performance metric, effective capacity, the simulation results show that GP provides more improved and stable performance over various node densities with the short completion time.