In cellular wireless communication systems, transmitted power is regulated to provide each user an acceptable connection by limiting the interference caused by other users. Several models have been considered including: (1) fixed base station assignment where the assignment of users to base stations is fixed, (2) minimum power assignment where a user is iteratively assigned to the base station at which its signal to interference ratio is highest, and (3) diversity reception, where a user's signal is combined from several or perhaps all base stations. For the above models, the uplink power control problem can be reduced to finding a vector p of users' transmitter powers satisfying p I(p) where the jth constraint p j I j (p) describes the interference that user j must overcome to achieve an acceptable connection. This work unifies results found for these systems by identifying common properties of the interference constraints. It is also shown that systems in which transmitter powers ...

We present a suite of algorithms for self-organization of wireless sensor networks, in which there is a scalably large number of mainly static nodes with highly constrained energy resources. The protocols further support slow mobility by a subset of the nodes, energy-efficient routing, and formation of ad hoc subnetworks for carrying out cooperative signal processing functions among a set of the nodes.

Transmit power control is a central technique for resource allocation and interference management in spread-spectrum wireless networks. With the increasing popularity of spread-spectrum as a multiple access technique, there has been significant research in the area in recent years. While power control has been considered traditionally as a means to counteract the harmful effect of channel fading, the more general emerging view is that it is a flexible mechanism to provide Quality-of-Service to individual users. In this paper, we will review the main threads of ideas and results in the recent development of this area, with a bias towards issues that have been the focus of our own research. For different receivers of varying complexity, we study both questions about optimal power control as well as the problem of characterizing the resulting network capacity. Although spread-spectrum communications has been traditionally viewed as a physical-layer subject, we argue that by suitable abstr...

We ask if the ubiquity of WiFi can be leveraged to provide cheap connectivity from moving vehicles for common applications such as Web browsing and VoIP. Driven by this question, we conduct a study of connection quality available to vehicular WiFi clients based on measurements from testbeds in two different cities. We find that current WiFi handoff methods, in which clients communicate with one basestation at a time, lead to frequent disruptions in connectivity. We also find that clients can overcome many disruptions by communicating with multiple basestations simultaneously. These findings lead us to develop ViFi, a protocol that opportunistically exploits basestation diversity to minimize disruptions and support interactive applications for mobile clients. ViFi uses a decentralized and lightweight probabilistic algorithm for coordination between participating basestations. Our evaluation using a twomonth long deployment and trace-driven simulations shows that its link-layer performance comes close to an ideal diversity-based protocol. Using two applications, VoIP and short TCP transfers, we show that the link layer performance improvement translates to better application performance. In our deployment, ViFi doubles the number of successful short TCP transfers and doubles the length of disruption-free VoIP sessions compared to an existing WiFi-style handoff protocol.

Abstract—In this paper, we study the effect of multihop relaying on the throughput of the downstream channel in cellular networks. In particular, we compare the throughput of the multihop system with that of the conventional cellular system, demonstrating the achievable throughput improvement by the multihop relaying. We also propose a hybrid control strategy for the multihop relaying, in which we advocate the use of both, the direct transmission and the multihop relaying. Our study shows that most of the throughput gain can be obtained with the use of a two- and three-hop relaying scheme. Substantial throughput improvement could be additionally obtained by operating the concurrent relaying transmission in conjunction with the nonconcurrent transmission. We also argue here that the multihop relaying technology can be utilized for mitigating unfairness in quality-of-service (QoS), which comes about due to the location-dependent signal quality. Our results show that the multihop system can provide more even QoS over the cell area. The multihop cellular network architecture can also be utilized as a self-configuring network mechanism that efficiently accommodates variability of traffic distribution. We have studied the throughput improvement for the uniform, as well as for the nonuniform traffic distribution, and we conclude that the use of multihop relaying in cellular networks would be relatively robust to changes in the actual traffic distribution. Index Terms—Ad hoc network, cellular network, code-division multiple access (CDMA), concurrent transmission, downstream channel, fairness, multihop relaying, self-configuring network, throughput. I.

The effect of soft and softer handoffs on codedivision multiple-access (CDMA) system capacity is evaluated for unsectorized and sectorized hexagonal cells according to an average bit energy-to-interference power spectral density, which corresponds to a bit-error rate (BER) of 10 0003 . The effect of imperfect sectorization on sectorization efficiency is also considered. On the reverse link, there is no capacity loss as no extra channels are needed to perform soft handoff, while the macrodiversity provided by soft handoff can improve the reverselink quality and extend the cell coverage. On the forward link, when soft handoff is employed in unsectorized cells, the capacity loss due to two traffic channels assigned to a user in the handoff zone is 0.2% or 1.1% for a voice activity factor of 3/8 or 1/2, respectively. As the forward-link capacity is higher than that of the reverse link, this small capacity loss does not affect the system capacity. For sectorized cells having three sectors per cell, there are overlapping coverage areas between sectors, where mobiles in these areas are subjected to an increase in cochannel interference. For an overlapping angle of 5 ffi , the sectorization efficiency is 0.96 and 0.7 for the reverse-link and forward-link systems, respectively. When soft and softer handoffs are employed, the forward-link sectorization efficiency is improved to 0.97. We find the application of soft and softer handoff improves not only the forward-link capacity, but also the signal-to-interference ratio (SIR) for mobiles near the cell and sector boundaries. Index Terms---CDMA, macrodiversity, sectorization efficiency, soft handoff, softer handoff. I.

Many analytical approaches have been proposed for handoff analysis based on hard handoff in mobile communication systems. In code-division multiple-access (CDMA) systems with soft handoff, mobile stations (MS's) within a soft-handoff region (SR) use multiple radio channels and receive their signals from multiple base stations (BS's) simultaneously. Therefore, SR's should be considered for handoff analysis in CDMA systems. In this paper, an analytical model for soft handoff in CDMA systems is developed by introducing an overlap_region between adjacent cells and the handoff call attempt rate and the channel holding times are derived. Applying these results to a nonprioritized CDMA system, the effects of soft handoff and the mean cell residual time are investigated and compared with hard handoff.

Traditional design rules for cellular networks are not directly applicable to code division multiple access (CDMA) networks where intercell interference is not mitigated by cell placement and careful frequency planning. For transmission quality requirements, a minimum signal-to-interference ratio (SIR) must be achieved. The base-station location, its pilot-signal power (which determines the size of the cell), and the transmission power of the mobiles all affect the received SIR. In addition, because of the need for power control in CDMA networks, large cells can cause a lot of interference to adjacent small cells, posing another constraint to design. In order to maximize the network capacity associated with a design, we develop a methodology to calculate the sensitivity of capacity to base-station location, pilot-signal power, and transmission power of each mobile. To alleviate the problem caused by different cell sizes, we introduce the power compensation factor, by which the nominal power of the mobiles in every cell is adjusted. We then use the calculated sensitivities in an iterative algorithm to determine the optimal locations of the base stations, pilot-signal powers, and power compensation factors in order to maximize capacity. We show examples of how networks using these design techniques provide higher capacity than those designed using traditional techniques.

Abstract — In this paper, we find bounds and approximations for the capacity of mobile cellular communication networks based on Code Division Multiple Access (CDMA). We develop efficient analytic techniques for capacity calculations of CDMA cellular networks. Each cell is modeled as an independent Å�� � queue and traffic capacity assessed based on the maximum Erlang traffic that leads to acceptable link quality with high probability. Subsequently, approximations and bounds for the outage probability and hence traffic capacity are obtained using Asymptotic Expansions and Large Deviations Theory. Numerical examples, considering uniform and Normalized Truncated Gaussian user density in the system are evaluated. The propagation model we consider takes care of distance and lognormal shadowing losses. 0-7803-7016-3/01/$10.00 ©2001 IEEE

The uplink coverage and capacity of CDMA cellular systems are intracell and intercell interference limited. In this work, we propose a practical multihop based cellular network design to enhance the uplink performance. The proposed design is based on dividing each cell into two regions where users belonging to an inner region communicate with the base station (BS) using one hop and users belonging to an outer region communicate with the BS using two hops. Each of the two regions is allocated a separate frequency channel to enable practical implementation and reduce interference. Analytic results show that intercell interference in CDMA cellular systems can be reduced by more than 75%. Moreover, a link budget analysis is performed to obtain coverage--capacity results with different receiver structures at the BS. Results show that with the single user detector (SUD) receiver, gains up to 100% in area coverage are achieved with moderate to low user loads. Furthermore, deploying multiuser detection to combat intracell interference, the proposed multihop based design achieves very high gains exceeding 100% in pole capacity and 300% in area coverage per cell.