Signal-to-interference Power Ratio Research Articles

Improved Channel Estimation and SIR Measurement in WCDMA Downlink Systems

The rake receiver performance of a direct-sequence code-division multiple-access (DS-CDMA) system can significantly be degraded unless the channel condition is properly estimated. Since the channel condition is time-varying and location-dependent, it is desirable to employ an adaptive channel estimator (ACE) that can properly adjust the bandwidth of the channel estimation filter (CEF) according to the channel condition such as the maximum Doppler frequency. To this end, we propose low-complexity ACE and signal-to-interference power ratio (SIR) estimator for wide-band CDMA downlink systems with and without the use of transmit antenna diversity. The proposed schemes adjust the bandwidth of the CEF by exploiting the correlation characteristics of the received pilot signal. The analytic design is verified by computer simulation. Simulation results show that the proposed ACE and SIR estimator can significantly improve the link performance for a wide range of channel condition, particularly when the channel condition is poor.

Accurate FFT Processing Window Timing Detection Based on Maximum SIR Criterion in OFCDM Wireless Access

This paper proposes an accurate Fast Fourier Transform (FFT) window timing detection method based on the maximum signal-to-interference power ratio (SIR) criterion taking into account the received signal and inter-symbol interference power according to different detected FFT window timings in Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access. In the proposed method, the SIR of the received signal is estimated using the desired signal power and inter-symbol interference power calculated based on the power delay profile, which is measured by the cross-correlation between the pilot symbol replica and the received signal. Furthermore, since the SIR is calculated only for the received path timing of the first path and those paths exceeding the guard interval duration, the computational complexity of the proposed method is low. Computer simulation results show that the proposed scheme reduces the required average received signal energy per symbol-to-noise power spectrum density ratio (E s /N 0 ) for achieving the average packet error rate of 10 -2 by approximately 1.0dB compared to the conventional method, which detects the forward path timing of the power delay profile (16QAM data modulation, six-path Rayleigh fading channel, and the maximum delay time of 3μsec (root mean squared (r.m.s.) delay spread of 0.86 μsec)).

Automatic calibration method of adaptive array with linear array utilizing signal circulation among antennas (ACT‐FL)

AbstractAn adaptive array for a frequency division duplex (FDD) system requires calibration among the antennas, the cables, and the transmitters and receivers to form the desired transmission directivity. In this paper, we propose the Automatic Calibration method of adaptive array using Transmitting signals for FDD systems with Linear array (ACT‐FL) by using the signal circulation among the antennas and not using any additional elements or external information for calibrating the antennas and cables. By studying the calibration accuracy of the ACT‐FL through analysis and tests including the mutual coupling of the antennas, we explain the applicable element spacing and the beam width in ACT‐FL. We also evaluate the signal‐to‐interference power ratio (SIR) at the interference arrival time from radiation pattern measurements by using a testbed implementing ACT‐FL and demonstrate the effectiveness of ACT‐FL. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(8): 20–31, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20105

Achievable-SIR-based predictive closed-loop power control in a CDMA mobile system

A power control algorithm with two prediction models based on an achievable signal-to-interference power ratio (SIR) has been proposed under a multipath Rayleigh fading environment in a code-division multiple-access (CDMA) mobile system. An achievable SIR is defined as the maximum-minimum SIR among all users at a particular time step. The corresponding mobile transmission powers are denoted as the "optimum transmission powers." In the individual power predictor (IPP) model, a linear transversal filter is assigned to each user. The output of the IPP, which is a linear combination of the optimum transmission powers of the mobile during the current and previous power measurement periods, predicts the optimum transmission power of the mobile in the next time step. In the global power predictor (GPP) model, a single predictor, constructed by a linear neural network, is used to predict the optimum transmission powers of all mobiles in the next time step. In both predictor models, the weights of the predictors are updated by using the recursive least squares algorithm. To further improve the performance, a reduced power-measurement period has been studied. Simulation results show that the proposed power control algorithm can achieve a lower outage probability and a smaller dynamic range of transmission power compared with a conventional power control scheme.

SIR weighting combining diversity for digital mobile communications

AbstractDiversity reception is a powerful technique to reduce the degradation of transmission quality caused by fading. One of the techniques, postdetection maximal‐ratio combiner (MRC), is not necessarily effective under cochannel interference, because received signal strength used as the weighting factor is not relative to the instantaneous signal‐to‐interference power ratio (SIR). The paper proposes an SIR estimation method using the matched filter and a diversity scheme using the estimated SIR as the weighting factor. The performance is evaluated theoretically and by means of computer simulations. The results show that the proposed SIR estimation method can estimate the accurate instantaneous SIR and that the BER characteristics of the proposed diversity scheme under cochannel interference realize better performances than those of MRC. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(7): 53–60, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/ecja.1111

Performance of generalized selection combining for mobile radio communications with mixed cochannel interferers

The performance of generalized selection combining (GSC) space diversity for mobile radio systems in the presence of multiple cochannel interferers is studied. Two cochannel interference models are considered: (1) L cochannel interferers consisting of L-N Nakagami-m (1960) interferers and N Rayleigh interferers and (2) L cochannel interferers in which each interferer follows Nakagami-m distribution for a fraction of time and Rayleigh distribution for the remaining of time. The fading parameters of the Nakagami-m interferers are limited to integer values only. The desired signal is assumed to be Rayleigh faded. Also, all the desired signals and the cochannel interferers received on each branch are independent of each other. Closed-form expressions are derived for the probability density functions (PDFs) of the instantaneous signal-to-interference power ratio (SIR) at the output of the GSC for the two cochannel interference models. Using these SIR PDFs, closed-form expression for evaluating the outage probability and the average bit error probability (BEP) are subsequently derived. A differential phase-shift keying scheme is considered in the derivation. Numerical results showing the influences of various system parameters on the outage probability and the average BEP are then presented.

Error Performance Evaluation of Wireless Communication Systems Using Maximal Ratio Combining with Multiple Interferers

In this paper we evaluate the error performance of wireless communication systems using M-branch maximal ratio combining (MRC) with multiple cochannel interference. Three cochannel interference models are considered: (A) L independent identically distributed (i.i.d.) Nakagami-m cochannel interferers; (B) L independent cochannel interferers consisting of L-N Nakagami-m interferers and N Rayleigh interferers; (C) L independent cochannel interferers in which each interferer follows Nakagami-m distribution for a fraction of time and Rayleigh distribution for the remaining time. In addition, the desired signal assumes Nakagami-m fading. This paper considers that an exponential correlation model is assumed for the desired signals received on each branch, while the interferers are assumed independent. Closed-form expressions are derived for the probability density functions (PDFs) of the instantaneous signal-to-interference power ratio (SIR) at the output of the MRC for the three interference models. Using these SIR PDFs, further closed-form expressions to evaluate the outage probability (OTP) and the average bit error probability (BEP) of differential phase-shift keying (DPSK) are derived. Numerical results showing the impacts of the system parameters on the OTP and the average BEP are then presented.

Predictive closed-loop power control in CDMA mobile systems

An achievable-SIR-based closed-loop power control scheme is proposed to maximise the minimum signal-to-interference power ratio (SIR). The proposed scheme is found to reduce the outage probability and also the dynamic range of the transmission power compared with the conventional power control scheme.

Cooperative signal reception and down-link beam forming in cellular mobile communications

A cooperative signal reception and down-link beam-forming algorithm is proposed for mobile communication systems employing phase-shift-keying (PSK) modulation. Down-link beam optimality is defined as maximizing the desired reference user's average received power while keeping the noise power plus total amount of average powers received by other users less than or equal to a certain constant level. The proposed algorithm requires neither the detection of other user's signals nor knowledge about the direction-of-arrivals (DOA)'s of the incident path components. Results of a series of exhaustive simulations are presented to demonstrate the overall performance of the proposed algorithm. For a hexagonal cell layout, the distribution of signal-to-interference power ratio (SIR) in a reference (central) cell with the optimal down-link beam is evaluated and compared with that with a unit gain omnidirectional antenna through computer simulations for an eight-element circular array. The beam-forming performances are also evaluated under several sets of practical parameter values with regard to the fading correlation.

Experimental results of localization of moving underwater signal by adaptive beamforming

The problem of weak moving signal localization and tracking in the presence of single motionless strong interference is investigated using real data of an underwater experiment in the Baltic sea (Sept. 1990) with a horizontal receiving array of 64 hydrophones and with two independent powerful narrowband sources imitating the signal and interference. Three simple adaptive beamforming methods were employed for the experimental data processing. The first one is based on the well-known projection approach to adaptive beamforming, the second method uses the adaptive canceler approach (also termed the dipole pattern method), and the third method combines these approaches. The signal-to-interference power ratio (SIR) threshold of the signal localization and tracking is evaluated by a special technique, which allows examination of the considered algorithms with change of the SIR in consecutive order. The results of the data processing show the high possibilities of signal localization in the presence of strong interference. The combined method performs better than the methods considered and enables localization of the signal source up to an SIR/spl sime/-25 dB. >

Performance of combined diversity reception and convolutional coding for QDPSK land mobile radio

Diversity reception and error correction coding are powerful techniques to combat multipath fading encountered in mobile radio communications. In order to improve the transmission performance of the /spl pi//4-shift QDPSK signal in mobile radio channels, the authors propose a new scheme of combined coding and diversity reception, i.e., combination of diversity reception employing code combining (CC) and convolutional coding employing error-and erasure correction Viterbi decoding. They also consider another combination scheme, i.e., combination of diversity reception employing postdetection maximal ratio combining (MRC) and convolutional coding employing hard decision Viterbi decoding. They theoretically analyze the performance of the schemes taking into account the additive white Gaussian noise (AWGN), random FM noise, co-channel interference (CCI), and intersymbol interference (ISI) due to multipath propagation delay spread. Numerical calculations are presented for the required average signal energy per bit-to-noise power spectral density ratio (E/sub b//N/sub 0/), required average signal-to-interference power ratio (SIR), tolerable maximum Doppler frequency, and tolerable rms delay spread needed to achieve a certain average BER. The spectrum efficiency of the cellular system is also calculated. >

Cochannel interference estimation for M-ary PSK modulated signals

Although the signal-to-interference power ratio (SIR) based criterion for diversity reception has been highlighted in the literature as the most effective method for reducing the effects of cochannel interference, it is often not clear how to measure this parameter in a practical context. This work addresses the problem of finding a way to determine the level of interference (due to frequency reuse) from neighbouring cells in a mobile telephone system, with M-ary PSK modulated signals and fast fading channel. The proposed parameter measures the quality of the received signal corrupted by additive white noise and cochannel interference, for any number of interferers. It is also suitable for high bit rate transmission, as in indoor mobile radio systems, since the proposed method requires sampling the received signal at just one sample/symbol.

Outage probabilities of diversity cellular systems with cochannel interference in Nakagami fading

Analytical, closed-form expressions for cellular outage probabilities in generalized Nakagami fading are derived for three practical diversity combining schemes. The outage is defined as the probability that the signal-to-interference power ratio (SIR) is less than a power protection ratio. The analysis considers L-branch equal gain (EG), selection (SC), and switched (SW) diversity combining schemes. The analyses are not limited to a single interferer, but rather assume the presence of multiple independent cochannel interferers. Previous results have used some approximations to study the performance of the EG combiner. A precise method is used to analyze the performance of an L-branch EG combiner. Selection diversity combining using the total power algorithm, the desired power algorithm, and the signal-to-interference power algorithm is analyzed. The effects of diversity on the reuse factor and on the spectrum efficiency of cellular mobile radio systems are considered in detail. The results for the Rayleigh fading channel are obtained and presented as a special case of the generalized Nakagami fading model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Steered Beam and LMS Interference Canceler Comparison

The performance of two kinds of interference cancelers is compared, namely, a constrained steered beam interference canceler (CSBIC) and a least mean square interference canceler (LMSIC). For simplicity, this is done for a two-element array. In our comparison we use the array output desired signal-to-interference power ratio (SIR) and the desired signal-to-noise ratio (SNR). These power ratios are obtained for the CSBIC and LMSIC under two sets of conditions: 1) The error in the assumed angle of incidence for the CSBIC is small, and the LMSIC operates in a codetracking mode. 2) The error in the assumed angle of incidence for the CSBIC is large, and the LMSIC operates in a code-acquisition mode. Comparison of the corresponding power ratios obtained under these two sets of conditions then establishes the condition under which it is more desirable to use a CBSIC as compared with an LMSIC.