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

In this communication, necessary and sufficient conditions are presented for the unique blind identification of possibly nonminimum phase channels driven by cyclostationary processes. Using a frequencydomain formulation, it is first shown that a channel can be identified by the second-order statistics of the observation if and only if the channel transfer function does not have special uniformly spaced zeros. This condition leads to several necessary and sufficient conditions on the observation spectra and the channel impulse response. Based on the frequency-domain formulation, a new identification algorithm is proposed

Blind channel identification based on second-order statistics: a frequency-domain approach

1 OFDM Background 2 2 Baseband Model 2 3 Block-Type Pilot Channel Estimation 4 4 Comb-Type Pilot Channel Estimation 7 5 Other Pilot-Aided Channel Estimations 9 6 Performance Evaluation 10 7 Conclusions 14 8 References 15 This application note gives an overview of the channel estimation strategies used in orthogonal frequency division multiplexing (OFDM) systems. Section 1 describes the protocols associated with OFDM systems and the problems posed by such systems. Section 2 through Section 5 describe the various types of channel estimation methods for use in such systems. The implementation complexity and system performance of the methods are studied and compared in Section 6, measuring performance in terms of symbol error rate (SER).

/pdf/channel-estimation-in-ofdm-systems-3yg0vdp0b6.pdf

Channel Estimation in OFDM Systems

Wireless communication is playing an important role in our daily life since it offers flexibility and mobility. New multimedia services demand data-rates of up to hundreds of Mbps and thus higher frequency bands are being explored to support these new high data rate services. However, to support mobility, handoff is a must in many of these networks and systems. In the mean time the 60 GHz band has received much attention due to its 5 GHz of the available spectrum globally. However, the 60 GHz channels face many challenges such as high attenuation and NLOS propagation. The high reduction in signal strength as a function of distance results in a small coverage area, thereby causing frequent handoffs for mobile terminals. In this paper, we discuss and compare handoff algorithms intended for WLAN, GSM, UMTS, etc. We study these algorithms from the point of view of their usability in 60 GHz networks and make recommendations for handoff algorithms in such networks.

/pdf/a-survey-on-handoffs-lessons-for-60-ghz-based-wireless-p056n71kqf.pdf

A Survey on Handoffs — Lessons for 60 GHz Based Wireless Systems

A comprehensive review on coordinated multi-point operation for LTE-A

A low-complexity probabilistic data association (PDA) multi-user detection algorithm is derived for space-time block coded multi-user systems, which can enhance the capacity of communication system by introducing co-channel users. Considered synchronous co-channel multi-users, each one is equipped with two transmit and two receive antennas, and then extended to multiple receive antennas to improve the performance. The simulation results show that the detection algorithm can reduce the intersymbol interference (ISI) greatly, and the system performance can get much improvement by using this strategy, which is very important for enlarging the communication capacity.

http://ieeexplore.ieee.org/iel5/10481/33236/01566806.pdf

Multi-user detection using space-time coding to improve systems capacity

In this paper, we study the resource allocation problem for the downlink of spatial-division multiple-access (SDMA) systems. We develop a general architecture to determine the optimal subset of users and their transmission rates. The constraints posed by the physical layer (in terms of spatial orthogonality) and by the link layer (in terms of QoS requirements) are jointly taken into consideration. As an implementation case, we propose efficient algorithms for systems that employ zeroforcing beamforming. Extensive simulations and analysis are performed to demonstrate the effectiveness of our proposal.

Cross-layer Resource Allocation for the Downlink of SDMA Systems

From the essence, HARQ is a joint multiple packets decoding technique. Two existing schemes, diversity combining and code combining, only make use of channel output symbols before decoding. Considering the correcting ability of FEC, output code combination is proposed. The output of decoder can be viewed as another output packet of transmission packet passing through a better channel. So it can be combined with new received channel erroneous packet. By means of analytical derivations and simulation, new combining scheme outperforms existing schemes. It greatly reduces system transmission delay without remarkable complexity increases

Performance Analysis of Multiple Packets Combining Decoding in HARQ

In cellular fixed relay networks diversity set update is an indispensable procedure in MDHO (macro diversity handover) mode. The paper proposes and compares two update algorithms for relay networks: an algorithm without direction information and a direction assisted algorithm. The average number of updates and the received signal strength are used as criteria for performance. The effects of the parameters in direction assisted algorithm are also well analyzed. The simulation results show that the direction assisted algorithm provides fewer update times and well received signal strength.

Diversity set update algorithm for MDHO in cellular fixed relay networks

To minimize the antenna costs in CDMA distributed antenna (DA) systems, a class of straightforward antenna dynamic selection (ADS) strategies for CDMA DA systems is proposed. In contrast to the traditional antenna static selection (ASS) method adopted in most of the literature that each "virtual cell" (VC) contains same number of antennas, ADS try to allocate as few antennas as possible to each VC according to the quality-of-service (QoS) requirement of each terminal. With antenna dynamic allocation in each VC, the obtained Eb/I 0 value of all terminals is kept just at the target value, which in turn minimizes the total antenna costs in CDMA DA systems. To investigate the real amount of performance improvement for ADS strategies, a system level simulator applied in a Manhattan-like environment is developed. Simulation results demonstrate effectiveness of ADS strategies, in comparison with the traditional ASS method

Wu Weiling

Papers

Multi-user detection using space-time coding to improve systems capacity

Cross-layer Resource Allocation for the Downlink of SDMA Systems

Performance Analysis of Multiple Packets Combining Decoding in HARQ

Diversity set update algorithm for MDHO in cellular fixed relay networks

Antenna dynamic selection strategies in CDMA distributed antenna systems