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In this study the relationship between the number of antenna elements (AEs) in a CDMA distributed antenna (DA) system and the yielding reverse link SIR is investigated by taking the power control dynamic range into account. In environments hostile to propagation, perfect power control may not be realized with a central antenna (CA), because this would require an impractically high dynamic range. This situation may yield a significant decrease in capacity. In such environments, the DA system is an ideal solution, since as the number of antenna elements increases, the dynamic range of the power control decreases. It is demonstrated that by using a DA system with as small as 4 AEs, a capacity increase of almost 30% is achievable, compared to the CA type. However, in a single-cell system once there are a sufficient number of antenna elements to implement perfect power control within a reasonable dynamic range, there is no need for additional antenna elements. Also, in a multi-cell system with CAs, the occasional transmissions at very high power levels in order to maintain perfect power control cause significant intercell interference. Since with the DA such situations are almost eliminated, the intercell interference is kept at a minimal level. Therefore, the DA is an ideal antenna type for both singleand multi-cell systems employing CDMA modulation.

The CDMA sectorized distributed antenna (SDA) is a novel antenna architecture which yields an increase in the reverse link capacity, in the order of the number of antenna elements used. In an SDA system, a power control algorithm that balances the SIR should be considered, since the conventional power-balanced power control algorithm results in considerable disparities among the SIR levels of different users. However, SIR-balancing for the SDA system is more complicated than that for the conventional central antenna systems due to macrodiversity. We use a power control algorithm which we refer to as SIR-balanced macro power control (SBMPC). SBMPC can be viewed as a special case of the power control algorithm introduced by Hanly (see IEEE Trans. Commun., vol.44, no.2, p.247-56, 1996) in the context of CDMA macrodiversity radio networks. In SBMPC, the set of equations to be solved are nonlinear (due to diversity) which makes the solutions for SIR-balancing algorithms, given in the literature, inapplicable. Therefore, we propose an iterative solution to the SBMPC algorithm which always converges. Because of the non-smooth convergence characteristics of the iterations, finding a suitable termination criterion for the iterations is a nontrivial problem. We suggest a multi-stage criterion which yields very low disparities among the SIR levels of different users for reasonably low number of iterations. Although the SBMPC algorithm and its iterative solution addressed in this paper are presented in the context of SDA systems, they may have wide applications. One such application is the power control problem in cellular systems employing macro diversity.

A new rapid acquisition scheme utilizing differentially coherent detection and PN matched filter is proposed. The system operates in burst mode transmission and the synchronization is achieved using a fixed preamble at the beginning of each data packet. The preamble is differentially modulated by a unique bit pattern, marker, which make it possible to perform code and frame synchronization simultaneously. Unlike other previous schemes, all preamble bits equally contribute to the acquisition process. The system performance measured in terms of packet loss probability for a given packet and preamble length. It is shown that this scheme greatly outperforms the conventional search-lock acquisition schemes which utilize non-coherent detection.

In this paper, a rapid acquisition technique, based on a parallel processing scheme is proposed. The proposed structure consists of a generalized differential detector utilizing N parallel matched filters followed by N multipliers. Under random code sequence assumption, an exact analysis of the performance for differentially-coherent detection in the presence of both thermal noise and self-noise is evaluated. This structure outperforms the classical non-coherent detection scheme by a margin of 4-5 dB in SNR. A new multiple-dwell decision scheme utilizing a single step sequence-based code phase estimation is also proposed and the mean acquisition times for both non-coherent and differential detectors are compared for these two decision schemes.

A modified multi-carrier (MC) DS-CDMA system has been proposed for use over slow multi-path fading channels with frequency selectivity in the reverse link transmission of the cellular network. Instead of transmitting data sub-streams uniformly through sub-channels, data sub-streams hop over sub-channels with the hopping patterns adaptively adjusted to the channel fading characteristics. The problem of determining the optimal hopping pattern is formulated as a multi-objective optimization problem, for which an efficient algorithm is designed to solve the problem practically. Simulation results show that the performance in terms of the average system bit error probability (BER) is better than that of a single carrier RAKE system, conventional MC CDMA systems applying moderate error protection and diversity systems with different combining techniques.

Differentially coherent detectors for acquisition of BPSK direct sequence spread-spectrum signals on an AWGN channel are analyzed. Under the random code sequence assumption, an exact analysis of the differentially-coherent detection performance for both full period correlation (FPC) and partial period correlation (PPC) is carried out and the results are compared with those of classical non-coherent detection. Finally the mean acquisition times for both single-dwell and multiple-dwell acquisition schemes are compared with their non-coherent counterparts. An improvement of 5 dB in the performance of the receiver is achieved.

Joint transmit beamforming, power control and the MMSE receiver are proposed for downlink channels of CDMA communication systems. Variability of the total transmit power while satisfying each user's quality of service is studied. We show that the total transmit power has a significant variation when we consider the combination of MMSE receiver and power control. When transmit beamforming is added, such variation is reduced significantly and great transmit power saving is achieved through the proposed scheme. The signature diversity concept is revealed for joint transmit beamforming and the MMSE receiver. An optimum MMSE, transmit beamforming and adaptive frequency hopping scheme is proposed to maximize the benefits of the MMSE receiver and transmit beamforming. Two sub-optimal algorithms are proposed to solve the optimization problem with reduced computational requirements.

The conceptual design of a system for Internet wireless access based on a large number of antenna sectors or fixed beams, with an overlapping structure, is proposed. The system utilizes spread spectrum modulation with time division multiplexing for transmissions from different overlapping antenna sectors. The fixed antenna beam structure is a practical approach to achieve space division multiplexing capacity gains with modest complexity. The time division multiplexing structure is shown to be a solution to the more general problem of designing sets of orthogonal signals for overlapping antenna sectors. We introduce the concept of time re-use as an analogue of frequency re-use in order to allocate time slots to clusters of antenna sectors. A frequency/time allocation strategy that depends on the terminal position within the cell and reduces interference is also introduced.

This paper presents interference analysis of a single frequency broadcast system (SFBS) in a power-controlled CDMA cellular network which operates in a low frequency band (LFB) for the reverse link and a high frequency band (HFB) for the forward link. Common to all forms of power control is the equalization of received power or received signal-to-interference ratio (SIR) at both the base station (BS) and portable (PT) disregarding the induced power distribution through the rest of the communication cell. As a result, an SFBS which operates in either the LFB or the HFB and is located somewhere inside the cell, may not benefit from power control, and is therefore susceptible to the "near-far" effects. Our emphasis is on dealing with the interference received at an SFBS receiver and on demonstrating the susceptibility of the SFBS receiver to the "near-far" problem in the LFB and the HFB. Both intracell and intercell interference scenarios are considered, with distance dependent and lognormal shadowing models adopted for propagation path loss. The end products are the cumulative distribution functions (CDFs) of the interference power received at the SFBS receiver in the LFB and the HFB for a PT uniformly distributed in a circular cell. These expressions are analytic for the distance dependent propagation model but require numerical integration when the lognormal shadowing model is introduced, and contribute toward the evaluation of outage probabilities of the SFBS receiver under various propagation conditions and location considerations.

It is reported by Hanly (see IEEE Trans. Commun., vol.44, no.2, p.247-56, 1996) that in the reverse link of a CDMA macrodiversity system a remarkable L-fold capacity (throughput) increase can be attained by using L antenna elements (AEs) provided that the spread spectrum bandwidth approaches infinity. In a finite-bandwidth system, however, the increase in capacity as a result of the utilization of multiple AEs will be less than linear due to the presence of the correlated interference effects. In this paper, a spatial correlated interference analysis is presented in order to investigate the effects of the system parameters on the severity of the correlated interference. The results presented indicate that the parameter which we defined as the chiplength ([speed of light]/[chip rate]) plays a role in macrodiversity systems (in regards to the correlation effects) similar to the role of the carrier wavelength in microdiversity systems. It is observed that in systems where the size of the service region is large enough to enable inter-AE distances many times larger than the chiplength, significant (close to linear) capacity gains can be achieved by employing macrodiversity with many AEs. If, on the other hand, the service region size is not large enough with respect to the chiplength, the returns due to macrodiversity will not be as high.

We present a hybrid FDD/SDD-WCDMA system architecture for supporting symmetric and asymmetric data users, with the former served by a cellular network and the latter served by broadcast systems. The asymmetric data users employ packet-mode access to transmit demand messages in relatively short bursts and are silent at other times, whereas the symmetric data users employ circuit-mode access. This imposes a significant challenge for performance optimization since accessing asymmetric data users can degrade the performance of currently active symmetric data users by introducing extra interference variations which reduce system capacity. We study the implementation and performance of a special version of iterative SIR-based power control algorithms in which currently active symmetric data users are protected from interference by accessing asymmetric data users. Moreover, as the accessing asymmetric data users are expected to have short duty cycles on the cellular network's reverse link, significant overhead may be required for iterative power control. We thus investigate the use of space diversity schemes to help reduce the high iteration overhead and access their performance jointly with the proposed iterative SIR-based power control algorithm.

The evolution of wireless communications is bringing the world to a different way of experiencing and producingmultimedia content. As a result, users are having an increasingly active role in the definition of networks. The chosen topic for the conference that was at the basis of this special issue was thus the pursuit of a really autonomous network infrastructure that will allow the efficient use of the spectrum and reduce energy requirements, exploring new possibilities like cognition and cooperation between users and systems. These developments bring excellent opportunities for the mobile community since new paradigms are needed to support the enormous surge of mobile data in present and future networks. The series of international symposia on Wireless Personal Multimedia Communications (WPMC) have always been a place where people from all over the world can bring their experiences together to develop knowledge about all aspects related to wireless networks

A modified multicarrier (MC) direct-sequence code-division multiple-access (DS-CDMA) system has been proposed for use over slow multipath fading channels with frequency selectivity in the reverse link transmission of a cellular network. Instead of transmitting data substreams uniformly through subchannels, data substreams hop over subchannels with the hopping patterns adaptively adjusted to the channel fading characteristics. The problem of determining the optimal hopping pattern is formulated as a multiobjective optimization problem, for which an efficient algorithm, based on the water-filling (WF) principle, is designed to solve the problem practically. Simulation results show that the performance in terms of the average bit-error probability (BEP) (over all users) is better than that of single carrier RAKE receiver systems, conventional MC CDMA systems applying moderate error protection, or diversity systems with different combining techniques.

Results on the modeling of interference in a radio communication network are presented, and performance measures for the link are given as a function of the distance for frequency hopping with M-ary frequency shift keying (FH/MFSK). It is assumed that a transmitter-receiver pair in a radio network is affected by a set of interferers, whose positions are modeled as a Poisson field in the plane. Assuming a 1/r/sup 4/ propagation power loss law, the probability of symbol error and the link capacity as a function of the distance between the transmitter and receiver are obtained. It is found that the symbol error probability is not dependent on the synchronization of the hopping times of the different users. >

Spreading code protocols for a distributed spread-spectrum packet radio network are presented. A distributed single-hop system (i.e. each terminal can hear all other terminals) with the users approximately synchronized and a set of prespecified spreading codes are presented. The spreading code protocol is a policy for choosing a spreading code to be used, given that a terminal has a packet to send, and a policy for monitoring spreading codes, given that a terminal is idle. A slotted system where a packet occupies a number of slots is considered, and two protocols that involve changing the spreading code of a transmission after an initial header is transmitted are presented. In one protocol, the header is transmitted on a common code, and in the other it is transmitted on a receiver-based code, the rest of the packet being transmitted on a transmitter-based code. In the receiving mode, a terminal monitors either a common code, in the first case, or a receiver-based code in the latter. Upon recognizing its own address and the source address, the receiver dynamically switches to a despreading code corresponding to the source. Throughput results are obtained for the case of geometrically distributed packet lengths. >

This paper studies the problem of designing a suitable pulse shape for teletext data transmission. The following four criteria are used: 1) Nyquist I criterion, 2) Nyquist II criterion, 3) degree of overshoots in the channel signal, and 4) robustness to sampling phase jitter. For system bandwidths less than the inverse-baud rate, it is not possible to satisfy all these criteria simultaneously; tradeoffs that have to be made are illustrated. Several candidate pulse shapes are given and a composite criterion developed. A pulse shape, which satisfies the Nyquist I criterion and is closest to satisfying the Nyquist II criterion, in a sum-of-squares-of-deviations sense, is recommended.

Various pulse shapes have been proposed for teletext data transmission. The effect of apportioning the different pulse shapes between the transmitter and the receiver is studied for the cases of a constraint on the power and a constraint on the peak value of the channel signal.

This paper is concerned with the graphical modeling of multi-hop spread spectrum packet radio networks. We show various network graphs, obtained using a graphics program, that illustrate typical connectivities that may be achieved for nominal values of the processing gain. The effects of the propagation power loss function and terminal transmission probability are also displayed. We introduce the notion of a soft link where the number of links included in the network depends on a link quality parameter.

In this paper we obtain the optimum transmission ranges to maximize throughput for a multi-hop spread spectrum network. In the analysis we model the network self-interference as a random variable which is equal to the sum of the interference power of all other terminals. For a spread spectrum network with an effective capacity equal to K simultaneous transmissions and an inverse fourth power propagation law we found that a terminal should transmit with a range so that on the average there are approximately 1.3?K terminals closer to the transmitter than the receiver. We found that for the inverse fourth power propagation law, the probability density of the interference power at a given terminal is the inverse Gaussian probability density. More generally, if the propagation law is an inverse ?th power (? ≫ 2), then the probability law of the interference power is the stable law of exponent 2/?.

The Steiner minimal tree (SMT) architecture is proposed for the wired-network infrastructure of wireless access networks. It is demonstrated that the wireless access networks having star or bus logical topologies can be realized within the proposed optimal SMT conduit structure. The SMT architecture results in a significant reduction in conduit length compared to the conventional star type, besides it provides more flexibility and robustness. For the systems which have logical bus topologies with centralized complexity, such as the distributed antenna (DA) systems, the SMT architecture is optimal in both cable and conduit lengths.

A modified carrier-sense multiple-access with collision detection (CSMA-CD) protocol which is suitable for high speed channels is presented and analyzed using the equilibrium point analysis (EPA) method. With the protocol each user has a finite buffer and does not transmit until it has accumulated a given number of packets, L. When this number is exceeded it will access the channel using a conventional CSMA-CD protocol and transmit all the packets in its buffer. This protocol is very simple to implement compared with multichannel protocols and results in higher throughput compared with slotted Aloha. The disadvantage is a larger delay, which is related to the parameter L, the packet arrival process, and the number of users. The delay can be reduced by dynamically controlling the parameter L and the retransmission probabilities of the protocol. The protocol is well suited for traffic arrival processes which are bursty where each burst of packets corresponds roughly to a message. Some performance results are given assuming a Bernoulli packet arrival process. >

Gives throughput results in terms of capacities per unit bandwidth for a multiaccess spread-spectrum communication system with a large number of users. Various spread-spectrum users are included. The direct sequence scheme with a sinc pulse as the chip pulse gives the maximum throughput of log/sub 2/ e(=1.44) bit/Hz. The frequency hopping schemes with M-ary frequency-shift keying have the smallest throughput; assuming detection with side information, for M=2 the throughput is equal to that of slotted ALOHA (e/sup -1/) and decreases as M increases.