Signal-to-interference Power Ratio Research Articles

CNN-based blind SIR classification framework for STPA-BAA spectrum superposing

Spectrum sharing in the spatial domain among the plurality of wireless communication systems should be addressed due to its exhaustion. We previously conceptualized a spectrum superposing enabled by subcarrier transmission power assignment (STPA) and blind adaptive array (BAA), where co-channel interference can be suppressed even without a priori information of interferer. However, it requires knowledge of input signal-to-interference power ratio (SIR) to realize completely blind operation. This paper proposes a blind SIR estimation framework by convolutional neural network (CNN) using power spectrum images. Simulation verifies the proposed scheme can maximize throughput performance based on SIR classification results with 97% accuracy.

Short-Packet Transmission in Irregular Repetition Slotted ALOHA System Over the Rayleigh Fading Channel

Random access systems are potential for Internet of Things in the future wireless communication network for its operational simplicity. Irregular repetition slotted ALOHA (IRSA) system is one of the high-efficiency random access systems. In this paper, performance analysis of the irregular repetition slotted ALOHA systems with short-packet, i.e. finite-blocklength, transmission for the quasi-static Rayleigh fading channel is given. A cumulative distribution function of signal-to-interference power ratio (SIR) is derived and thus a closed-form expression of an average packet error probability (PEP) at the SIR with short packets for the Rayleigh fading channel is given. The closed-form expression makes it possible to optimize the degree distributions at a specific blocklength in the sense that the systems give the maximum system load.

Interference Gaussianization: Time-Domain Inter-Symbol Spreading for Blind Adaptive Array Signal Source Identification

This paper proposes a novel blind adaptive array (BAA) interference suppression scheme incorporated with a time-domain symbol spreading (TISS). It can expand an operational region of BAA irrespective of input signal-to-interference power ratio (SIR) conditions. Independent component analysis (ICA) and constant modulus algorithm (CMA) are expected as the promising BAA approaches to suppress unknown interference which is extensively caused due to the small cell densification and spectrum superposing between a plurality of wireless communication systems. These BAA algorithms basically require an input SIR to be larger than 0 dB to suppress interference by capturing the desired signal appropriately. The proposed scheme applies TISS to the transmission signal for the desired user and then de-spreads it at the receiver side. It Gaussianizes statistical inherence of the interference signals and can bring beneficial effects; reducing the kurtosis for ICA as well as collapsing the constant envelope properties for CMA. Such intentional modification to the interference signals can improve the capture performance of the desired signal and realize its effective identification even at SIR <; 0 dB. Its fundamental effectiveness is presented through various perspectives such as input SIR, symbol amount, and modulation orders.

Low‐complexity subspace method for I/Q imbalance estimation in low‐IF receivers with unknown fading

AbstractIn low‐intermediate‐frequency (low‐IF) receivers, I/Q imbalance (IQI) causes interference on the desired signal from the blocker signal transmitted over the image frequencies. Conventional approaches for pilot‐aided IQI estimation in zero‐IF receivers are not applicable to low‐IF receivers, where the image interference is unknown at the receiver. We propose a low‐complexity subspace method for the estimation of IQI parameters in low‐IF receivers in the presence of unknown fading, where we utilize knowledge of the pilots to null out the signal part. This reduces the variance of the sample mean estimate and leads to faster convergence. The proposed nulling method offers significantly better image rejection at low input signal‐to‐interference power ratio (SIR) than existing methods. Performance analysis of the output SIR as well as computer simulations are also provided.

Thompson Sampling-Based Channel Selection Through Density Estimation Aided by Stochastic Geometry

We propose a sophisticated channel selection scheme based on multi-armed bandits and stochastic geometry analysis. In the proposed scheme, a typical user attempts to estimate the density of active interferers for every channel via the repeated observations of signal-to-interference power ratio (SIR), which demonstrates the randomness induced by randomized interference sources and fading effects. The purpose of this study involves enabling a typical user to identify the channel with the lowest density of active interferers while considering the communication quality during exploration. To resolve the trade-off between obtaining more observations on uncertain channels and using a channel that appears better, we employ a bandit algorithm called Thompson sampling (TS), which is known for its empirical effectiveness. We consider two ideas to enhance TS. First, noticing that the SIR distribution derived through stochastic geometry is useful for updating the posterior distribution of the density, we propose incorporating the SIR distribution into TS to estimate the density of active interferers. Second, TS requires sampling from the posterior distribution of the density for each channel, while it is significantly more complicated for the posterior distribution of the density to generate samples than well-known distribution. The results indicate that this type of sampling process is achieved via the Markov chain Monte Carlo method (MCMC). The simulation results indicate that the proposed method enables a typical user to determine the channel with the lowest density more efficiently than the TS without density estimation aided by stochastic geometry, and $\epsilon $ -greedy strategies.

Soft sectored fractional frequency reuse in LTE-advanced networks

Fractional Frequency Reuse (FFR) has been suggested as an Inter Cell Interference Coordination (ICIC) technique in Orthogonal Frequency Division Multiple Access (OFDMA), where the cell is separated into internal and external regions. The inner means that it is close to eNB, while the outer indicates closeness to the boundaries of the cell. The main idea of FFR is to divide the cell’s bandwidth into partitions for reducing the cell interference from both inner users and the adjacent cells. The FFR has three main types including Strict FFR, Soft FFR and Sectored FFR (SFFR). This work proposes a hybrid Soft Sectored Fractional Frequency Reuse (SSFFR), which analyzes the uplink worst case Signal to Interference power Ratio (SIR). In addition, the effect of power control exponent, path loss exponent and inner radius are studied, and SSFFR is compared with SFFR. Simulation results show that, the higher SIR achieved by outer-SSFFR, enables to enhance the cell edge transmission through interference management.

Stabilised blind interference suppression of constant modulus‐based adaptive array over Rayleigh fading channels by initial antenna selection

This article proposes an initial antenna selection for constant modulus-based blind interference suppression algorithms to stabilise their prominent interference suppression performance. Constant modulus algorithm (CMA) is a well-known blind adaptive array scheme, but it cannot suppress the interference when signal-to-interference power ratio (SIR) is <0 dB. It faces strong limits on their applicable region over Rayleigh fading channels where instantaneous channel gain fluctuates over 10 dB range. Even if the expected desired signal strength is larger than interference, CMA may still miscapture the interference and incorrectly suppress the desired signal. The authors’ proposal is simplified approach to select the antenna element whose reception power is maximal. Certain antenna element can be expected to capture the desired signal precisely under the condition where SIR is statistically positive, so that the CMA processor can utilise it as an initial input. This condition will be ensured by increasing antenna element number, supported by the trends that base station antenna elements are going massive. Computer simulations verifies improved interference suppression performance provided by the proposed scheme. This article also verified applicability for multi-modulus algorithm to accommodate M-ary quadrature amplitude modulation (QAM) use.

Suppressing the effect of ICI power using dual sinc pulses in OFDM-based systems

Sensitivity to frequency offset in orthogonal frequency division multiplexing (OFDM)-based systems allow unwanted interference among the subcarriers, which results in intercarrier interference (ICI). A novel family of Nyquist-I pulses, named dual sinc pulses (DSPs), is proposed herein having three new design parameters, giving additional degrees of freedom to minimize ICI power in OFDM-based systems. Several Nyquist-I pulses have been studied and implemented to deal with the problem of frequency offset in OFDM-based systems. In this paper, we investigate the performance of DSPs in terms of ICI power, signal-to-interference power ratio (SIR), and bit error rate (BER) in OFDM-based systems. The frequency responses of the DSPs are studied by adjusting the values of the new design parameters. Theoretical and simulation results presented herein show that DSPs outperform other existing pulses in OFDM-based systems, in terms of ICI power, SIR power, and BER.

Análisis y estudio de los efectos de la interferencia de co-canal sobre la tasa de error de bit media para sistemas con multiplexación espacial

En este artículo, el desempeño de un sistema con multiplexación espacial (SM, por sus siglas en inglés, Spatial Multiplexing) es investigado, teniendo en consideración un canal con desvanecimiento Rayleigh y la presencia de interferencia de co-canal (ICC). Primeramente, expresiones para evaluar la tasa de error de bit media (BER, por sus siglas en inglés, Bit Error Rate) para sistemas con SM que hacen uso de modulaciones BPSK y QPSK son obtenidas, dichas expresiones se encuentran en función de la relación señal-ruido (Eb/N0), y de la relación señal-interferencia (SIR, por sus siglas en inglés, Signal-to-Interference power Ratio), considerando la presencia de un interferente de co-canal dominante. Validaciones de las expresiones analíticas son realizadas a través de simulaciones de Monte-Carlo. Los resultados muestran que la ICC causa una degradación notable en la BER, la cual varía de acuerdo a la SIR. Los resultados obtenidos en este artículo, pueden ser aplicados para redes celulares con SM para diferente número de antenas transmisoras.

OFDMA 시스템에서 SFO와 CFO 저감 기법에 관한 연구

Abstract Recently, orthogonal frequency-division multiplexing(OFDM), with clusters of subcarriers allocated to different subscribers(often referred to as OFDMA), has gained much attention for its ability in enabling multiple-access wireless multimedia communications. In such systems, carrier frequency offsets (CFOs) can destroy the orthogonality among subcarriers. And the mismatch in sampling frequencies between transmitter and receiver can lead to serious degradation due to the loss of orthogonality between the subcarriers. As a result, multiuser interference (MUI) along with significant performance degradation can be induced. In this paper, we present a scheme to compensate for the SFOs and CFOs at the base station of an OFDMA system. A novel sampling frequency offset estimation algorithm is proposed, which is based on the repetition of a symbol at the communication start-up. Then, circular convolutions are employed to generate the interference after the discrete Fourier transform processing, which is then removed from the original received signal to increase the signal to interference power ratio(SIR). Simulation result shows that the proposed scheme can improve system performance.

Downlink performance limitations of cellular systems with coordinated base stations and mismatched precoder

Coordination of base stations is a promising technique for reducing inter-cell interference in next-generation cellular systems. For the downlink of such systems, the authors study the degradation of zero-forcing precoded transmissions caused by imperfect channel estimation and channel variation over time. They derive exact expressions for the mean power of the desired signal received by an arbitrary user and of the interference caused by the mismatched precoder. By using these expressions, they show that for attaining a given signal-to-interference power ratio (SIR) these systems are limited by a maximum feedback delay of updated channel state information. Finally, they present a procedure to calculate the maximum tolerable feedback delay and to determine the separation between the non-precoded pilot symbols for guaranteeing a desired SIR.

Analyzing the capacity of wireless ad hoc networks

The total amount of capacity that can be obtained from a network is an essential performance metric. However, in wireless ad hoc networks, the dynamic topology and stochastic variations in channel characteristics, makes it difficult to analytically determine this metric. In this paper we develop analytical closed form expression for the network capacity. First the cumulative distribution function (CDF) of the signal to interference power ratio (SIR) at each receiver is derived analytically. Then, the capacity of the network is studied and closed form expressions are determined. Also by examining the effect of the outage threshold, β, it is shown that, less simultaneous communications, each with a higher rate can result in higher total capacity.

D2D 통신 시스템을 위한 CAZAC 시퀀스 기반 링크 스케줄링 기법

대표적인 D2D (Device-to-Device) 통신 시스템 중 하나인 Qualcomm사의 FlashLinQ 시스템에서는 링크 스케줄링 과정을 낮은 복잡도로 실현할 수 있도록 하기 위해 단일-톤 (single-tone) 신호를 이용한 우선순위 및 SIR (Signal-to-Interference power Ratio) 기반의 링크 스케줄링 기법을 수행한다. 하지만 다중 경로 채널 환경에서는 주파수 선택적 페이딩의 영향으로 단일-톤 위치에서와 실제 데이터가 전송되는 전체 대역에서의 수신 전력 간 오차가 발생할 수 있으며, 이는 공평성 측면에서 문제가 될 뿐만 아니라 셀 전체 전송률 상의 손실을 일으킬 수 있다. 따라서, 본 논문에서는 이러한 문제를 해결하기 위해 CAZAC (Constant Amplitude Zero Auto-Correlation) 시퀀스의 상관 특성을 이용해 전체 대역에 대한 SIR 에 가까운 값을 획득할 수 있는 링크 스케줄링 기법을 제안한다. 제안 기법은 전체 대역을 다수의 sub-block 으로 구분하고 각 sub-block 마다 링크의 우선순위에 해당하는 순환 오프셋 (cyclic offset) 을 적용한 CAZAC 시퀀스를 전 대역에 걸쳐 전송하여, 수신 신호와 참조 신호간의 순환 상호 상관 연산 (cyclic cross-correlation)을 통해 전체 대역에 대한 SIR 에 근접한 값을 획득할 수 있다. FlashLinQ, one of the typical D2D communication systems developed by Qualcomm, considers a single-tone communication based distributed channel-aware link scheduling method to realize the link scheduling process with low control overheads. However, considering the frequency selective fading effect of practical multi-path channel, the single-tone based SIR estimation causes a critical scheduling error problem because the received single-tone signal has quite different channel gain at each sub-carrier location. In order to overcome this problem, we propose a novel link scheduling method based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence for D2D communication system. In the proposed method, each link has a unique offset value set for the generation of CAZAC sequences. CAZAC sequences with the cyclic offsets are transmitted using multiple sub-blocks in the entire bandwidth, and then each device can obtain nearly full-band SIR using a good cyclic cross-correlation property of CAZAC sequence.

Impact on Inter-Cell Interference of Reference Signal for Interference Rejection Combining Receiver in LTE-Advanced Downlink

This paper investigates the dominant impact on the interference rejection combining (IRC) receiver due to the downlink reference signal (RS) based covariance matrix estimation scheme. When the transmission modes using the cell-specific RS (CRS) in LTE/LTE-Advanced are assumed, the property of the non-precoded CRS is different from that of the data signals. This difference poses two problems to the IRC receiver. First, it results in different levels of accuracy for the RS based covariance matrix estimation. Second, assuming the case where the CRS from the interfering cell collides with the desired data signals of the serving cell, the IRC receiver cannot perfectly suppress this CRS interference. The results of simulations assuming two transmitter and receiver antenna branches show that the impact of the CRS-to-CRS collision among cells is greater than that for the CRS interference on the desired data signals especially in closed-loop multiple-input multiple-output (MIMO) systems, from the viewpoint of the output signal-to-interference-plus-noise power ratio (SINR). However, the IRC receiver improves the user throughput by more than 20% compared to the conventional maximal ratio combining (MRC) receiver under the simulation assumptions made in this paper even when the CRS-to-CRS collision is assumed. Furthermore, the results verify the observations made in regard to the impact of inter-cell interference of the CRS for various average received signal-to-noise power ratio (SNR) and signal-to-interference power ratio (SIR) environments. key words: LTE-Advanced, interference rejection combining, inter-cell interference, reference signal, turbo equalizer

Outage threshold extraction for maximising the capacity of wireless ad hoc networks

In this article, the authors develop an ‘analytical closed-form expression’ for the outage capacity of a wireless ad hoc network. First, a series of practical modulation schemes including binary phase shift keying (BPSK) and quadrature amplitude modulation (QAM) are considered. Then, a proper formulation for the total network capacity is presented based on the cumulative distribution function (CDF) of the signal to interference power ratio (SIR). A closed-form expression for this CDF is also analytically derived. Subsequently, the outage capacity of the network is examined. By investigating the effect of the outage threshold, it is shown that an optimum threshold value exists that maximises the outage capacity. This optimum value is obtained in the networks with different number of nodes. The analytical results are verified by conducting simulation studies.

A Comparison of Adaline and MLP Neural Network based Predictors in SIR Estimation in Mobile DS/CDMA Systems

In this paper we compare the response of linear and nonlinear neural network-based prediction schemes in prediction of received Signal-to-Interference Power Ratio (SIR) in Direct Sequence Code Division Multiple Access (DS/CDMA) systems. The nonlinear predictor is Multilayer Perceptron MLP and the linear predictor is an Adaptive Linear (Adaline) predictor. We solve the problem of complexity by using the Minimum Mean Squared Error (MMSE) principle to select the optimal predictors. The optimized Adaline predictor is compared to optimized MLP by employing noisy Rayleigh fading signals with 1.8 GHZ carrier frequency in an urban environment. The results show that the Adaline predictor can estimates SIR with the same error as MLP when the user has the velocity of 5 km/h and 60 km/h but by increasing the velocity up-to 120 km/h the mean squared error of MLP is two times more than Adaline predictor. This makes the Adaline predictor (with lower complexity) more suitable than MLP for closed-loop power control where efficient and accurate identification of the time-varying inverse dynamics of the multi path fading channel is required. Keywords—Power control, neural networks, DS/CDMA mobile communication systems.

A scheme for cancelling intercarrier interference using conjugate transmission in multicarrier communication systems

To mitigate intercarrier interference (ICI), a two-path algorithm is developed for multicarrier communication systems, including orthogonal frequency division multiplexing (OFDM) systems. The first path employs the regular OFDM algorithm. The second path uses the conjugate transmission of the first path. The combination of both paths forms a conjugate ICI cancellation scheme at the receiver. This conjugate cancellation (CC) scheme provides (1) a high signal to interference power ratio (SIR) in the presence of small frequency offsets (50 dB and 33 dB higher than that of the regular OFDM and linear self-cancellation algorithms (Y. Zhao and S.-G. Haggman, 2001), (J. Armstrong, 1999), respectively, at DeltafT = 0.1% of subcarrier frequency spacing); (2) better bit error rate (BER) performance in both additive white Gaussian noise (AWGN) and fading channels; (3) backward compatibility with the existing OFDM system; (4) no channel equalization is needed for reducing ICI, a simple low cost receiver without increasing system complexity. Although the two-path transmission reduces bandwidth efficiency, the disadvantage can be balanced by increasing signal alphabet sizes

Unified Analysis for SIR-Based Power and Rate Control in Multipath Fading Channels

In this paper, we present a unified analysis on various signal-to-interference power ratio (SIR)-based power and rate control schemes in independent and nonidentical multipath fading channels. We study wireless direct sequence code division multiple access (DS-CDMA) systems with RAKE reception and derive new expressions for a mobile user's average SIR, average transmission power, and average data rate in terms of the probability distribution of the SIR. The performance of SIR-based combined power/rate control, power control, rate control, truncated power control, and truncated rate control schemes in independent and nonidentical Rayleigh fading channels is presented and compared. By substituting appropriate SIR distributions, this general mathematical framework can be applied to other fading channels such as the Nakagami, Rician, and lognormal channels

Interference Cancellation with DFE in Frequency Domain for OFDM Systems with Insufficient CP

In OFDM systems, employing a cyclic prefix (CP) as the guard interval is a simple way to combat the inter-symbol interference (ISI) and the inter-carrier interference (ICI), however it reduces the transmission efficiency of the system, especially for some channels with a very long delay spread. In this paper, we consider the OFDM system with insufficient CP, much more efficient than conventional OFDM systems. First, we present the system mathematical model and give the ISI and ICI analysis. Then the signal-to-interference power ratio (SIR) performance is presented. To reduce the ISI and ICI due to the insufficient CP, we develop a minimum-mean-square-error decision feedback equalizer (MMSE_DFE). Based on the MMSE criterion, the optimum feedforward and feedback filter coefficients are derived. For time-varying channel, to avoid brute force matrix inversion in conventional schemes, we propose an adaptive LMS based solution to update the filtering coefficients by tracing the channel variation. Since the high complexity of MMSE-DFE, a reduced complexity scheme, ordered successive partial interference cancellation DFE (OSPIC-DFE), is developed. From the performance comparison between the MMSE-DFE and the OSPIC-DFE, we see that the latter is very near to the former. Finally the simulation shows these proposed methods are highly effective in combating ISI and ICI with low complexity.

An Interference-Cancellation Scheme for Carrier Frequency Offsets Correction in OFDMA Systems

Recently, orthogonal frequency-division multiplexing (OFDM), with clusters of subcarriers allocated to different subscribers (often referred to as OFDMA), has gained much attention for its ability in enabling multiple-access wireless multimedia communications. In such systems, carrier frequency offsets (CFOs) can destroy the orthogonality among subcarriers. As a result, multiuser interference (MUI) along with significant performance degradation can be induced. In this paper, we present a scheme to compensate for the CFOs at the base station of an OFDMA system. In the proposed scheme, circular convolutions are employed to generate the interference after the discrete Fourier transform processing, which is then removed from the original received signal to increase the signal-to-interference power ratio (SIR). Both SIR analysis and simulation results will show that the proposed scheme can significantly improve system performance.