Two-branch Selection Diversity Research Articles

Multipath Interference Reduction In Wireless Radio Systems Using Two-Branch Selection Diversity

Fading is a major impairment when transmitting a signal in wireless communication channel. It is caused by multipath propagation. That is signals from different paths can constructively or destructively interfere with each other. Thus, it becomes very necessary to reduce this effect, to transmit the signal effectively to the receiver This work explains the concept of multipath interference as well as technique used in reducing such, which include the two branch selection diversity that analytically derives an upper bound for the output power of two-sensor branch- selection reception, based on an empirically proven “geometric model” of the wireless propagation channel. Diversity techniques are very useful to improve the performance of high speed wireless channel to transmit data and nformation.

Switching rates of two-branch selection diversity in correlated Doppler fading

The switching rate of a correlated dual branch selection diversity combiner in Rayleigh and Rician fading is derived in noise-free conditions. Balanced and unbalanced branches are considered. Numerical results are presented for a space-diversity system with horizontally spaced omnidirectional antennas at a mobile station.

Switching rates of two-branch selection diversity in κ-μ and α-μ distributed fadings

An analytical expression for the switching rate of a dual branch selection diversity combiner in kappa-mu and alpha-mu distributed fadings is derived. Independent and identically distributed (i.i.d.) kappa-mu as well as alpha-mu fading channels are considered. The switching rates for dual i.i.d. Rayleigh, Rician and Nakagami-m fading channels are special cases of the switching rate for dual i.i.d. kappa-mu fading channels. Similarly, the general switching rates for dual alpha-mu fading channels also include special cases such as Rayleigh, Nakagami-m, and Weibull fading channels.

Field trial results for high-speed wireless indoor data communications

This paper reports on the development of a flexible 5-MBd equalized M-QAM testbed for high-speed wireless data communications. The unit operates in real time and was field tested in typical indoor environments. A total of 3600 independent experiments were conducted using the testbed where one of 4-, 16-, 64-QAM constellations were transmitted, and the performance as a function of adaptive equalization and antenna selection diversity was studied. The experimental results presented here help put previous simulation and analytical results into perspective and demonstrate some of the performance bounds associated with a practical implementation. The field trial results show that with only 10-mW of transmit power, reliable 10-Mbit/s data communication can take place in between rooms with a coverage radius of 17 m, and better than 15% outage at an uncoded bit error rate (BER) of 10/sup -3/. The addition of two-branch antenna selection diversity to the system would allow 10-Mbit/s transmission at better than 3% outage and 20-Mbit/s transmission at 10% outage in the same environment. Moreover, 30-Mbit/s data transmission is feasible when both the transmitter and receiver are located within the same room, albeit at higher outage levels. In general, the results demonstrate the tremendous impact that adaptive equalization can have on the achievable performance of indoor links. Average SNR was improved anywhere from 8 dB to 12 dB depending on the particular environment and data rate. The impact on the outage performance, however, was much more dramatic.

An experimental TDMA transmission system using 1.5 GHz-band π/4 shifted QPSK

The π/4-shift QPSK transmission system with TDMA scheme is constructed and an experiment is conducted, aiming at the digital cellular automobile telephone system. Various detection methods are first compared and it is decided that differential detection is advantageous, considering the operation in TDMA system where the burst modulated wave must be demodulated. Then, by varying the bandwidth of the receiving filter in the differential detection demodulator, the biterror rate and the adjacent channel emission are examined using simulation. The optimal receiver bandwidth is determined. In the differential detection, the bit-error rate depends greatly on the carrier frequency drift. A highspeed automatic frequency control (AFC) circuit is newly proposed to solve this problem. The post-detection, two-branch selection diversity demodulator is experimentally constructed and a satisfactory performance is obtained, with the deviation from the theoretical value being 2.3 dB under the static condition, and the diversity gain is 6 to 7 dB. Based on those results, it is experimentally verified that the π/4-shifted QPSK differential detection with TDMA scheme is practically useful.

QDPSK signal transmission performance with postdetection selection diversity reception in land mobile radio

The bit error rate (BER) performance of 16-128 kb/s Nyquist raised-cosine filtered quaternary differential phase-shift keying (RC-QDPSK) signal transmission was experimentally investigated. Two-branch postdetection selection diversity reception was employed. Measured results are presented for the BER performance due to additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread. Field BER measurements were also conducted at a carrier frequency of 1.45 GHz in an area characterized by high-rise buildings and in an area surrounded by mountains. The results show that postdetection selection diversity is a simple yet powerful technique to improve the BER performance in fading mobile radio channels. >

Postdetection selection diversity with unequal branch signal power compensation

A new postdetection two-branch selection diversity scheme is proposed that can reduce the influence of unequal average signal powers of the two branches. A BER analysis is presented for π/4-shift QDPSK assuming very slow Rayleigh fading channel. It is shown that if the difference in average powers is 6dB, the BER performance due to cochannel interference can be improved by about l.3dB and is almost identical to that of the equal average power case.

Discriminator-MLSE Detection of a GTFM Signal in the Presence of Fast Rayleigh Fading

This paper examines the influence of fast Rayleigh fading and cochannel interference on GTFM with discriminator-MLSE detection using a hardware fading simulator. The degradation in BER performance, due to fading, can be largely recovered by using two-branch selection diversity. The resultant bit error patterns are also presented.

Diversity improvement of voice signal transmission using postdetection selection combining in land mobile radio

This paper describes the effect of postdetection selection combining diversity on voice signal transmission for wide-band PM and narrow-band PM in a Rayleigh fading environment. First, the baseband average SNR versus the average CNR for a two-branch selection diversity with the syllabic compandor is derived in a closed form including the effect of the envelope correlation coefficient. Then, the dual selection diversity receiver, which shares an envelope detector with two branches in time division, and its performance are described. Finally, laboratory tests using a Rayleigh fading simulator are carried out with the result that an effective diversity improvement is obtained for a cross correlation coefficient in the range from 0 to 0.5.

Diversity Improvement of Voice Signal Transmission Using Postdetection Selection Combining in Land Mobile Radio

This paper describes the effect of postdetection selection combining diversity on voice signal transmission for wide-band PM and narrow-band PM in a Rayleigh fading environment. First, the baseband average SNR versus the average CNR for a twobranch selection diversity with the syllabic Compandor is derived in a closed form including the effect of the envelope Correlation coefficient. Then, the dual selection diversity receiver, which shares an envelope detector with two branches in time division, and its performance are described. Finally, laboratory tests using a Rayleigh fading simulator are carried out with the result that an effective diversity improvement is obtained for a cross correlation coefficient in the range from 0 to 0.5.

Time division adaptive retransmission for reducing signal impairments in portable radiotelephones

Multiple-antenna receiving diversity was shown previously to be effective in mitigating the effects of random angular orientation and multipath radio propagation for portable radiotelephones. It is shown that time-division adaptive retransmission used with appropriate antenna configurations can also mitigate these effects. The retransmission configurations require fewer antennas than the receiving diversity configurations for a given improvement in relative signal-to-noise ratio (S/N). Cumulative distributions of S/N were determined for adaptive retransmission and diversity using random orientation and multipath propagation models. Distributions of S/N for systems with two antennas at the portable set and two appropriately polarized antennas at the portable radiotelephone terminal (PORT) are similar to distributions for two-branch selection diversity in the fixed-orientation mobile radio environment. Systems with one portable antenna and two PORT antennas have distributions with slopes similiar to two-branch mobile radio distributions but the distributions for the portables range from 3 to 7 dB worse.

Antenna Diversity Performance in Mitigating the Effects of Portable Radiotelephone Orientation and Multipath Propagation

Antenna diversity can mitigate signal impairments caused by random angular orientation and multipath radio propagation when using portable radiotelephones. Cumulative distributions of signal-to-noise ratio ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S/N</tex> ) were determined for antenna diversity using realistic orientation and multipath propagation models. In a random orientation and multipath propagation environment with -6 dB average crosspolarization coupling, two-branch selection diversity with two perpendicular antennas yields an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S/N</tex> distribution with the same slope as two-branch selection diversity in the fixed-oriented mobile radio environment. The distribution for random orientation is about 4.5 dB worse, however, than the mobile radio distribution.

Random FM in Mobile Radio with Diversity

The probability density function and autocorrelation function of random FM in a mobile radio system are derived for the case where postdetection selection diversity is used. Closed-form solutions for the autocorrelation function have been found for no diversity and two-branch diversity and infinite series expansions for higher orders. The use of two-branch selection diversity is shown to reduce the random FM by 13.5 dB in a typical case, with a further 2.5-dB reduction when three branches are used. The effect of other forms of diversity on random FM is briefly assessed, but not pursued in detail.

A comparison of specific space diversity techniques for reduction of fast fading in UHF mobile radio systems

Over the past few years a variety of space diversity system techniques have been considered for the purpose of reducing the rapid fading encountered in microwave mobile radio systems. Basic diversity methods are first reviewed in the framework of mobile propagation effects, and then specific techniques are compared from the standpoint of transmitter power required to achieve a certain performance. Criteria of comparison used included baseband SNR while moving and reliability when the vehicle stops at random. System parameters are type and order of diversity and transmission bandwidth. Tradeoffs between performance properties and system parameters are indicated. The calculations show that relatively modest use of diversity techniques can afford savings in transmitter power of 10-20 dB. For example, at a range of 2 mi, to obtain 30-dB baseband SNR while moving and 99.9-percent reliability when stopped requires a transmitted power of 8 W for a conventional FM system with no diversity. Two-branch selection diversity provides the same performance for a transmitter power of only 300 mW.