It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

This paper is on beamforming in wireless relay networks with perfect channel information at relays, the receiver, and the transmitter if there is a direct link between the transmitter and receiver. It is assumed that every node in the network has its own power constraint. A two-step amplify-and-forward protocol is used, in which the transmitter and relays not only use match filters to form a beam at the receiver but also adaptively adjust their transmit powers according to the channel strength information. For a network with any number of relays and no direct link, the optimal power control is solved analytically. The complexity of finding the exact solution is linear in the number of relays. Our results show that the transmitter should always use its maximal power and the optimal power used at a relay is not a binary function. It can take any value between zero and its maximum transmit power. Also, this value depends on the quality of all other channels in addition to the relay's own channels. Despite this coupling fact, distributive strategies are proposed in which, with the aid of a low-rate broadcast from the receiver, a relay needs only its own channel information to implement the optimal power control. Simulated performance shows that network beamforming achieves the maximal diversity and outperforms other existing schemes. Then, beamforming in networks with a direct link are considered. We show that when the direct link exists during the first step only, the optimal power control is the same as that of networks with no direct link. For networks with a direct link during the second step, recursive numerical algorithms are proposed to solve the power control problem. Simulation shows that by adjusting the transmitter and relays' powers adaptively, network performance is significantly improved.

Network Beamforming Using Relays with Perfect Channel Information

This paper deals with beamforming in wireless relay networks with perfect channel information at the relays, receiver, and transmitter if there is a direct link between the transmitter and receiver. It is assumed that every node in the network has its own power constraint. A two-step amplify-and-forward protocol is used, in which the transmitter and relays not only use match filters to form a beam at the receiver but also adaptively adjust their transmit powers according to the channel strength information. For networks with no direct link, an algorithm is proposed to analytically find the exact solution with linear (in network size) complexity. It is shown that the transmitter should always use its maximal power while the optimal power of a relay ca.n take any value between zero and its maxima. Also, this value depends on the quality of all other channels in addition to the relay's own. Despite this coupling fact, distributive strategies are proposed in which, with the aid of a low-rate receiver broadcast, a relay needs only its own channel information to implement the optimal power control. Then, beamforming in networks with a direct link is considered. When the direct link exists during the first step only, the optimal power control is the same as that of networks with no direct link. For networks with a direct link during the second step only and both steps, recursive numerical algorithms are proposed. Simulation shows that network beamforming achieves the maximal diversity order and outperforms other existing schemes.

Network Beamforming Using Relays With Perfect Channel Information

We investigate spatial interference statistics for multigigabit outdoor mesh networks operating in the unlicensed 60-GHz "millimeter (mm) wave" band. The links in such networks are highly directional: Because of the small carrier wavelength (an order of magnitude smaller than those for existing cellular and wireless local area networks), narrow beams are essential for overcoming higher path loss and can be implemented using compact electronically steerable antenna arrays. Directionality drastically reduces interference, but it also leads to "deafness," making implicit coordination using carrier sense infeasible. In this paper, we make a quantitative case for rethinking medium access control (MAC) design in such settings. Unlike existing MAC protocols for omnidirectional networks, where the focus is on interference management, we contend that MAC design for 60-GHz mesh networks can essentially ignore interference and must focus instead on the challenge of scheduling half-duplex transmissions with deaf neighbors. Our main contribution is an analytical framework for estimating the collision probability in such networks as a function of the antenna patterns and the density of simultaneously transmitting nodes. The numerical results from our interference analysis show that highly directional links can indeed be modeled as pseudowired, in that the collision probability is small even with a significant density of transmitters. Furthermore, simulation of a rudimentary directional slotted Aloha protocol shows that packet losses due to failed coordination are an order of magnitude higher than those due to collisions, confirming our analytical results and highlighting the need for more sophisticated coordination mechanisms.

Interference analysis for highly directional 60-GHz mesh networks: the case for rethinking medium access control

An important issue of supporting multi-user video streaming over wireless networks is how to optimize the systematic scheduling by intelligently utilizing the available network resources while, at the same time, to meet each video's Quality of Service (QoS) requirement. In this work, we study the problem of video streaming over multi-channel multi-radio multihop wireless networks, and develop fully distributed scheduling schemes with the goals of minimizing the video distortion and achieving certain fairness. We first construct a general distortion model according to the network?s transmission mechanism, as well as the rate distortion characteristics of the video. Then, we formulate the scheduling as a convex optimization problem, and propose a distributed solution by jointly considering channel assignment, rate allocation, and routing. Specifically, each stream strikes a balance between the selfish motivation of minimizing video distortion and the global performance of minimizing network congestions. Furthermore, we extend the proposed scheduling scheme by addressing the fairness problem. Unlike prior works that target at users' bandwidth or demand fairness, we propose a media-aware distortion-fairness strategy which is aware of the characteristics of video frames and ensures max-min distortion-fairness sharing among multiple video streams. We provide extensive simulation results which demonstrate the effectiveness of our proposed schemes.

/pdf/distributed-scheduling-scheme-for-video-streaming-over-multi-2ci78j4vv7.pdf

Distributed scheduling scheme for video streaming over multi-channel multi-radio multi-hop wireless networks

Error probabilities for various unbalanced DS-CDMA systems are calculated using the standard Gaussian approximation, improved Gaussian approximation and the Fourier series based schemes. A scarcely populated system, a system with a dominant interferer, a system in a fading channel and a multimedia system with a single high processing gain user are considered. It is seen that the standard Gaussian approximation in all of these cases gives inaccurate results, especially when the number of users active in the system is low. The improved Gaussian approximation on the other hand, gives more accurate results for a scarcely populated system and a system with a dominant interferer. For systems in fading channels and multimedia systems, neither of the Gaussian approximations are accurate. For all of these cases, the Fourier series based scheme gives very accurate results without computational complexity.

Calculating error probabilities for DS-CDMA systems: when not to use the Gaussian approximation

The aim of this paper is to analysis the new assisted GPS (A-GPS) architecture based on SUPL (secure user plane location). This architecture improves performance of A-GPS based location estimation approaches. We provide comparative field test results of the developed system with the conventional GPS in terms of both the position accuracy and the TTFF (time to first fix) delay times. We have also examined the effectiveness of initial position estimation on the TTFF and the accuracy of calculated position. Field tests are conducted on a real GSM network in urban areas and indoor environments. Executed analysis has provided that the developed SUPL based A-GPS system achieves high-performance on estimation accuracy and faster TTFF.

Secure User-Plane Location (SUPL) Architecture For Assisted GPS (A-GPS)

It is envisioned that access networks will be mostly wireless in the future. Hence, it is of interest to consider extensions of the datagram congestion control protocol (DCCP) for wireless networks. This paper focuses on the problems of video streaming over DCCP in the wireless domain and proposes a cross-layer solution in which the wireless packet loss information available in the medium access (MAC) layer is utilized by DCCP to distinguish congestion losses from wireless losses and behave accordingly. Tests performed with our modified DCCP confirm that using cross-layer loss information prevents unnecessary rate decreases and results in better video streaming experiences.

Video streaming over wireless DCCP

We have developed a CDMA based residential indoor system that uses time division duplexing with dynamic channel allocation. The proposed indoor system shares the same frequency band as the outdoor ANSI-008 based cellular PCS network and operates within its coverage area. Due to the time division duplexing nature of the residential system, both the forward and reverse link signals are transmitted in the same frequency band in different time slots. In principle the indoor system may operate either in the PCS uplink or the PCS downlink frequency band. After extensive simulations, we conclude that underlaying such a system to the existing ANSI-008 PCS system is feasible. Addition of such a system would ultimately increase the CDMA capacity substantially.

A dynamic channel allocation based TDD DS CDMA residential indoor system

Use of direct sequence code division multiple access (DS CDMA) has been the object of much attention in the research and development of a multi-service personal communications network. The performance of such a system is usually given in terms of the bit error rate as a function of the number of active users for a given signal to noise ratio. We have investigated the degradation in the performance of a BPSK modulated, bi-phase spread DS CDMA system due to synchronization errors. A Fourier series approach has been used to find an infinite series representation for the probability of error when both chip timing and carrier phase errors are present. The analysis requires the characteristic functions of both the multiple access interference and self interference and these functions have been expressed in terms of the special functions of mathematical physics. Computation of the infinite series is very fast as a whole bit error curve can be generated in minutes on a Sparc IPX workstation. The infinite series is also compared with the standard Gaussian approximation and an alternative Gaussian approximation found in the literature. The series is then used to assess the reduction in system capacity when synchronization errors are present in the system. We have expressed this degradation in the system performance as an effective processing gain reduction.

M.O. Sunay

Papers

Calculating error probabilities for DS-CDMA systems: when not to use the Gaussian approximation

Secure User-Plane Location (SUPL) Architecture For Assisted GPS (A-GPS)

Video streaming over wireless DCCP

A dynamic channel allocation based TDD DS CDMA residential indoor system

Sensitivity of a DS CDMA system with long PN sequences to synchronization errors