Classical coverage models, adopted for second-generation cellular systems, are not suited for planning universal mobile telecommunication system (UMTS) base station (BS) location because they are only based on signal predictions and do not consider the traffic distribution, the signal quality requirements, and the power control (PC) mechanism. In this paper, we propose discrete optimization models and algorithms aimed at supporting the decisions in the process of planning where to locate new BSs. These models consider the signal-to-interference ratio as quality measure and capture at different levels of detail the signal quality requirements and the specific PC mechanism of the wideband CDMA air interface. Given that these UMTS BS location models are nonpolynomial (NP)-hard, we propose two randomized greedy procedures and a tabu search algorithm for the uplink (mobile to BS) direction which is the most stringent one from the traffic point of view in the presence of balanced connections such as voice calls. The different models, which take into account installation costs, signal quality and traffic coverage, and the corresponding algorithms, are compared on families of small to large-size instances generated by using classical propagation models.

We present a framework for resource control in CDMA networks carrying elastic tra#c, considering both the uplink and the downlink direction. The framework is based on microeconomics and congestion pricing, and seeks to exploit the joint control of the transmission rate and the signal quality in order to achieve e#cient utilization of network resources, in a distributed and decentralized manner. An important feature of the framework is that it incorporates both the congestion for shared resources in wireless and wired networks, and the cost of battery power at mobile hosts. We prove that for elastic tra#c, where users value only their average throughput, the user's net utility maximization problem can be decomposed into two simpler problems: one involving the selection of the optimal signal quality, and one involving the selection of the optimal transmission rate. Based on this result, the selection of signal quality can be performed as done today using outer loop power control, while rate adaptation can be integrated with rate adaptation at the transport layer.

Abstract — We explore the feasibility of designing an outdoor cellular network based on the IEEE 802.11 specification. Since the standard is intended for wireless local-area networks (WLAN), there are many technical challenges when applying the air interface to the outdoor environment. We study here how the 802.11 medium access control (MAC) protocol can be applied and how it performs in the outdoor network. By exploiting the fact that timeout intervals are not explicitly specified, without modifying the standard, we propose a new timing structure for the distribution coordination function (DCF) and the handshake of request-to-send (RTS) and clear-to-send (CTS) to handle increased signal propagation delay in the outdoor network. We find that the DCF and RTS/CTS protocols as specified in the standard continue to work properly for a link distance up to 6 km. Our analysis reveals that the DCF performance degrades

Ever increasing data traffic and limited capacity are major causes for congestion in current cellular systems. This paper presents a new architecture for the next generation wireless systems based on the integration of the cellular infrastructure and modern Ad-hoc relaying technologies. The new architecture can efficiently balance traffic loads between cells by using Ad-hoc relay stations (ARS) to relay traffic from one cell to another cell dynamically. This can not only increase a system's capacity cost-effectively, but also reduce transmission power for mobile hosts, and provide services for shadow areas. In this paper, we present the architectural concept including its basic operations and principle benefits. We also propose a seed-growing approach for ARS placement, and discuss the upper boundon the number of seed ARS's needed in the system. We evaluate the performance improvement of the new architecture through analysis and simulations. 1 Introduction Ever increasing data traffi...

Abstract—In this paper, a multiple-input–multiple-output (MIMO) extension for a third-generation (3G) wireless system is described. The integration of MIMO concepts within the existing UMTS standard and the associated space–time RAKE receiver are explained. An analysis is followed by a description of an actual experimental MIMO transmitter and receiver architecture, both realized on digital signal processors (DSPs) and FPGAs within a precommercial OneBTS base station. It uses four transmit and four receive antennas to achieve downlink data rates up to 1 Mb/s per user with a spreading factor of 32 and the UMTS chip rate of 3.84 MHz. Furthermore, different MIMO detectors are evaluated, comparing their performance and complexity. System performance is evaluated through simulations and indoor over-the-air measurements. Capacity and bit-error rate measurement results are presented. Index Terms—OneBTS, rapid prototyping, third-generation (3G), UMTS, wireless multiple-input–multiple-output (MIMO) systems. I.

In this paper we compute the uplink capacity of power-control CDMA mobile networks with an idealized power control, that contain best-effort type applications, i.e. applications whose transmission rate can be controlled. An arriving best-effort call is assumed to have a fixed amount of traffic to send, so the transmission rate assigned to it determines the duration of the call. We allow for multi-services (so that mobile stations have different quality of service requirements) . Unlike some previous published work where soft blocking was considered (and the system was thus allowed to operate beyond capacity), we assume that a call admission mechanism is implemented in order to prevent a new call to arrive when the system is already saturated. This guarantees the quality of service of ongoing calls. Our first result is that slowing the transmission rates in the case of a single cell with homogeneous quality of service characteristics increases capacity. This suggests that there is a limit capacity that can be approached when slowing down the transmission rates. We identify this limit and show that it has the following property: as long as the arrival rate of information is below some level, blocking probability can become arbitrarily small by su#ciently slowing down the transmission rates. We then extend the results to the general heterogeneous and multi-cell case.

The presence of "unwanted" (or background) tra#c in the Internet is a well-known fact. In principle any network that has been engineered without taking its presence into account might experience troubles during periods of massive exposure to unwanted traffic, e.g. during large-scale infections. A concrete example was provided by the spreading of Code-Red-II in 2001, which caused several routers crashes worldwide. Similar events might take place in 3G networks as well, with further potential complications arising from their high functional complexity and the scarcity of radio resources. For example, under certain hypothetical network configuration settings unwanted traffic, and specifically scanning traffic from infected Mobile Stations, can cause large-scale wastage of logical resources, and in extreme cases even starvation. Unwanted traffic is present nowdays also in GPRS/UMTS, mainly due to the widespread use of 3G connect cards for laptops. We urge the research community and network operators to consider the issue of 3G robustness to unwanted traffic as a prominent research area.

Abstract — We propose to use joint network-channel coding based on turbo codes for the multiple-access relay channel. Such a system can be used for the cooperative uplink for two mobile stations to a base station with the help of a relay. We compare the proposed system with a distributed turbo code for the relay channel and with a system which uses separate network-channel coding for the multiple-access relay channel. Simulation results confirm that the systems with network coding for the multipleaccess relay channel gain cooperative diversity compared to the system with the distributed turbo code for the relay channel. Moreover, the results show that joint network-channel coding outperforms separate network-channel coding. The reason for this is that the redundancy which is contained in the transmission of the relay can be exploited more efficiently with joint networkchannel coding. I.

Abstract—In mobile communications, the movement of terminals renders the multipath channel time varying. Even though the faded amplitudes are fast varying, the delays can be considered as stationary on a large temporal scale. In this paper, we propose a new subspace-based method that estimates the channel response from multiple slots by capitalizing on these different varying rates without explicitly computing the delays of the multipath. The temporal subspace is obtained from multiple single-slot training-based estimates of the (single-user or multiuser) channel response. Provided that the number of slots is large enough, the time basis can be calculated with any accuracy. As a consequence, the mean-square error on the channel response depends only on the number of fast-varying parameters that have to be estimated in a slot-by-slot fashion. Performance analysis and simulations confirm the expected benefits of the multislot approach in improving the efficiency of systems with short training sequences. Index Terms—Code-division multiple access (CDMA), delay estimation, fading channels, multipath channels, multiuser channels, reduced rank processing, subspace tracking, time-division multiple access (TDMA), time-varying channels, training. I.

We present a model based on congestion pricing for resource control in wireless CDMA networks carrying traffic streams that have fixed-rate requirements, but can adapt their signal quality. Our model considers the resource usage constraint in the uplink of CDMA networks, and does not differentiate users based on their distance from the base station. We compare our model with other economic models that have appeared in the literature, identifying their similarities and differences. Our investigations include the effects of a mobile's distance and the wireless network's load on the target signal quality, the transmission power, and the user benefit.