Curtis C. Ling

A low-complexity antenna diversity receiver suitable for TDMA handset implementation

This paper introduces a low-complexity antenna diversity receiver suitable for TDMA handset implementation. The receiver employs two branches of diversity, and is capable of adaptively choosing among three different diversity techniques which are implemented in a single design which we refer to as a multi-diversity receiver. It consists of a single conventional wireless digital receiver chain augmented with a few additional low-cost passive RF components and minor control circuits. We present algorithms for efficient co-phasing and equal-gain combining, as well as a novel cochannel interference-reduction combining algorithm. These are implemented in a system design simulation which conforms to the PACS (Personal Access Communication System) standard. We then present simulation link performance for selection diversity (SD), equal-gain combining (EGC) and interference-reduction combining (IRC) under Raleigh fading, flat fading with cochannel interference and selective fading conditions. The results show that EGC and IRC yield a signal-to-noise ratio (SNR) improvement of 1 dB and a signal-to-interference ratio (SIR) improvement 4 dB-/spl sim/5.5 dB, respectively, compared with SD. The receiver also lowers the irreducible word error rate due to multipath delay spread when the Doppler shift is small. These results are compared with the results from other research.

Rate determination algorithms in IS-95 forward traffic channels

According to the IS-95 CDMA standard, the transmit data rate can vary from frame to frame depending on the speech activity. However, the receiver does not know the data rate of the received frames. Conventionally, the receiver has to decode the received frame four times corresponding to the four possible data rates in rate set 1 or rate set 2 so as to obtain the correct decoded frame. Two rate determination algorithms for using 8 kbps (rate set 1) and 13 kbps (rate set 2) speech codecs in the forward traffic channel are introduced. The idea of maximum-likelihood estimation is employed in these two algorithms to determine the data rate. By using these algorithms, the received frame can be decoded once only corresponding to the determined rate instead of four times. Consequently, the decoding complexity and the power consumption at the receiver can be significantly reduced. From our analysis, the worst-case complexity and the average power consumption can be saved by a factor of 2 and 5, respectively.

Low-Complexity Antenna Diversity Receivers for Mobile Wireless Applications

This paper describes low-complexity diversity receiver techniques suitable forhandsets and other wireless mobile applications. The techniques areillustrated using two branches of diversity feeding aparameter-combining RF circuit at the front-end, followed by asingle digital receiver chain. A baseband processing algorithm isused to adjust the front-end combining parameters, allowing the receiver toadaptively choose among three different diversity techniques. The method aspresented is primarily targeted for indoor environments where handset movementis slow and delay spread is small. We present algorithms for efficientco-phasing and equal-gain combining as well as a novel cochannelinterference-reduction algorithm. These are implemented in a system simulationat 900 MHz which conforms to the PACS standard. Link performance for selectiondiversity (SD), equal-gain combining (EGC), and interference-reductioncombining (IRC) is presented. The algorithms performance is compared withoptimal combining parameters, and its performance as a function of Dopplerfrequency is enhanced. The results show that EGC and IRC yield asignal-to-noise improvement of 1 dB and a signal-to-interference improvementof 4 to 5.5 dB respectively, compared with SD. The receiver also lowers theirreducible word error rate due to multipath delay spread for Doppler shiftsof 6 Hz and below. Finally, algorithm behavior is characterized and discussed.

Low-complexity antenna diversity receivers for WCDMA handsets

A low-complexity antenna diversity architecture using a single receiver chain together with a novel combining algorithm suitable for WCDMA systems is designed to improve handset performance in the mobile downlink. Simulation results are presented comparing different diversity receiver configurations under several channel conditions. System sensitivity to the Doppler frequency and correlation between diversity branches are investigated. Both selection diversity (SD) and a receiver using two front-ends (2FE) are compared with the combining algorithm. The results show that the combining architecture outperforms SD, which is a proposed candidate for WCDMA handset by a gain of about 1.25 dB, while being inferior to 2FE by only 0.75 dB.

Wireless personal communications in Hong Kong: a university perspective

The position of Hong Kong as a financial and commercial center of southeast Asia depends critically on telecommunications. A well-developed telecommunication infrastructure is in place providing high-quality services for both wireline and wireless communications. Hong Kongs application of wireless communicators is among the most active in the world. This has been encouraged by several factors, including the inconvenience of face-to-face communications for people on the move in a densely populated city, the relatively low cost of using wireless communications, the proactive attitude of regulators to adopting new technologies, a population that is not afraid of using new technologies to gain convenience, and strong competition among service providers. The Hong Kong Office of the Telecommunications Authority has awarded licenses for the new PCS-related services, and the government is also increasing funding support for research activities. In this article, the authors first outline Hong Kongs current regulatory and service status in wireless communications and the plan for opening up new PCS. The rest of the article focuses on the research effort in a new university, including development of receivers.

Low power ACS unit design for the Viterbi decoder [CDMA wireless systems]

In this paper, we address the issues of designing low power VLSI implementation of the Viterbi decoder. We propose a new VLSI architecture for carrying out the add-compare-select (ACS) operation for the Viterbi decoder which can reduce the complexity of the computation. Also a novel pre-computational architecture is proposed to further reduce the power consumption of the ACS unit.

Low Power Rake Receiver and Viterbi Decoder Design for CDMA Applications

In this paper, we address the issues of designing lowpower VLSI implementation of the Code DivisionMultiple Access (CDMA) receiver. Among all the digitalfunctional blocks of a CDMA receiver, the RAKEreceiver and the Viterbi decoder are the mostcomputational intensive and hence consume most of thepower. In this work, we propose new VLSI architecturesfor these two functional blocks which consumesignificantly lower power. In particular, were-organize the structure of the pilot-aided RAKEdemodulator to reduce the operational frequency of thearithmetic components and we propose a newAdd-Compare-Select (ACS) architecture for the Viterbidecoder which can reduce the complexity of thecomputation. Also a novel pre-computationalarchitecture is proposed to further reduce the powerconsumption of the ACS unit. Experimental results showsignificant reduction in power consumption.

Low-complexity antenna diversity receivers with SINR enhancement for WCDMA handsets

This paper introduces a combining algorithm for WCDMA handsets using a single front-end circuitry to enhance signal-to-interference-and-noise ratio (SINR). The proposed algorithm can have a gain of about 6 dB over selection diversity, the conventional design for multiple antenna system for handsets. Analytical equations based on a multipath channel model are derived and simulation results and performance evaluation comparing several diversity receivers are also presented.

The fading characteristics of distributed antennas for indoor wireless systems

Distributed antennas have been suggested as a possible method for providing reliable coverage for indoor wireless communications. One aspect of the distributed antenna system however has not been well investigated. This concerns possible interference effects (resulting in fading) between antennas within the distributed antenna. In this paper we analyze and simulate the potential effects of this fading to exactly determine whether it will play a significant role in the coverage provided by distributed antennas. We also compare our simulations to actual measurement results in the mobile telephone bands. Particular design criteria are then suggested.

Non-radial non-uniformity in chemo-mechanical polishing

Within-wafer non-uniformity due to chemo-mechanical polishing (CMP) is classified in this paper as belonging to two classes: radially symmetric (radial), and not radially symmetric (non-radial). While radial non-uniformity has been well-treated both theoretically and empirically in the literature, the equally important problem of non-radial non-uniformity has received little attention. We identify the significance of the latter here through a series of CMP experiments, and propose a straightforward intermediate solution.