Adjacent Channel Interference Research Articles

OFDM Pilot Design for Channel Estimation with Null Edge Subcarriers

Wireless communication systems are increasingly adopting orthogonal frequency division multiplexing (OFDM) to enable efficient high-data rate transmissions. Such systems often employ pilot symbols to estimate wireless channels, and null subcarriers on band edges to reduce adjacent channel interference. Recent work has focused on designing the pilot sequence to improve channel estimation performance. In this paper, we present a new pilot design for OFDM systems based on a arbitrary-order polynomial parameterization of the pilot subcarrier indices. We show our design achieves better performance than existing methods. Theoretical models and simulated performance demonstrate the increased accuracy of our design.

DTV 대역에서 WiBro와 무선랜의 상호공존성에 관한 연구

본 논문은 DTV 주파수 대역(185 MHz, 481 MHz, 687 MHz)에 WiBro와 무선랜 서비스가 동일 채널 및 인접 채널에 할당되는 시나리오를 가정한 후, Monte-Carlo 기반의 Spectrum Engineering Advanced Monte Carlo Analysis Tool(SEAMCAT)을 이용한 간섭 분석을 통해 최적의 주파수 대역을 제시하였다. 분석 내용으로 WiBro Mobile Station과 무선랜 User Equipment 사이의 요구되는 보호거리 및 보호 대역, WiBro Mobile Station/Base Station 및 무선랜 User Equipment 의 허용 송신 파워를 분석하였다. 분석 결과, 주파수 대역 185 MHz에 할당할 경우가 상대적으로 잠재적 간섭이 가장 큰 경우이고 697 MHz의 할당이 최적의 주파수 대역으로 분석되었다. 본 분석결과는 향후 DTV 주파수 대역에 WiBro와 무선랜의 할당에 유용하게 활용될 것으로 기대된다. Mutual Interference scenarios between Wireless Broadband (WiBro) and Wireless LAN (WLAN) in DTV bands are assumed. Co-channel interference and adjacent channel interference are respectively evaluated in terms of carrier to interference ratio (C/I) by using Spectrum Engineering Advanced Monte Carlo Analysis Tool (SEAMCAT) based on the Monte-Carlo simulation method. For the simulation, three frequencies such as 185 MHz, 481 MHz and 687 MHz are chosen. Analysis results indicate that interference situation of using frequency of 185 MHz is the worst case, which requires longer protection distance between WiBro MS and WLAN User Equipment (UE), lower transmit power of WiBro Mobile Station (MS) and WiBro Base Station (BS) and WLAN UE and larger guard band. Comparing to cases of using frequency of 185 MHz and 481 MHz, interference situation of using frequency of 687 MHz is slighter. Therefore, using frequency of 687 MHz is easier for coexistence between WiBro and WLAN. Analysis results can be used as reference and guideline when planning the deployment of WiBro and WLAN in DTV bands.

WCDMA multiservice uplink capacity of highways cigar-shaped microcells with adjacent channel interference

The multiservice uplink capacity and the interference (intracellular and intercellular) statistics (mean and variance) of the sectors of the cigar-shaped wide band code division multiple access microcell are studied, taking into account the impact of the adjacent channel interference. A model of five microcells (10 sectors) is used in the analysis. The two-slope propagation loss model with lognormal shadowing is used in the analysis. The capacity and the interference statistics of the microcell are studied for different values of the distance between the base station of the two systems (system under study and the system using the adjacent channel). It is noted that for a distance between the base stations of both systems of 100 m, the capacity reduction due to the adjacent channel interference is lower than 3.4% (for data service). For collocated systems, capacity reduction is negligible. It is noticed that increasing the adjacent channel leakage power ratio from 30 to 40 dB will increase the sector uplink capacity by only 3%. Copyright © 2011 John Wiley & Sons, Ltd.

광대역 멀티미디어 시스템을 위한 다채널 중간 주파수 송수신기 설계 및 성능 분석

본 논문에서는 초고속 광대역 무선 멀티미디어 서비스를 양방향으로 제공하는 시스템을 위한 다 채널 중간주파수 변환 모듈을 설계하고 성능을 분석하였다. 먼저 송수신기를 구성하는 각 부분에 대한 기본적인 이론을 소개하고 이를 바탕으로 송수신부를 설계하고 각 모듈별로 무 변조, 변조시의 특성 및 광 대역 다 채널 신호의 발생과정에서의 채널에 따른 특성을 시간 및 주파수 영역에서 측정하였다. 송수신부의 국부 발진 신호의 위상잡음 특성은 70dBc/kHz 이하로 특성이 우수하다. 대역내 주파수 특성은 송수신 특성이 평탄하게 측정되었다. 한편 송수신기의 자동이득조절 기능은 상당히 우수한 것으로 나타났다. 또한 이웃채널 간섭의 영향과 스퓨리어스 방사에 대한 성능분석도 하였다. In this paper, the multichannel intermediate frequency transceiver for broadband multimedia system is designed and the experimental results are analyzed. Basic elements of the transceiver such as frequency synthesizer, amplifier, mixer, automatic gain control amplifier are introduced. The analysis technique described here applies not only to amplifier but also to any other nonlinear components such as mixers and frequency doubler. Through the investigation of the power spectrum density of the transmitted signal, the phase noise of the local oscillator is evaluated below 70 dBc/kHz. The frequency characteristics of the modulated signal is flat within the system bandwidth. Also the effects of adjacent channel interference and supurious emission are analyzed. And the function of automatic gain control amplifier is well operated.

Can cognitive radio technology help solve some difficult spectrum management issues by creating "virtual guardbands"?

The fundamental goal of spectrum management is to maximize use of the spectrum. This generally is taken to mean use without "harmful interference". The first problem in avoiding harmful interference has classically been to avoid having two signals on the same frequency that can cause interference to each other at locations where interference-free use is desired. This has been the classical issue in spectrum management. However, cochannel interference is not the only interference mechanism in practical radio systems. Adjacent channel interference, receiver desensitization, and receiver-generated intermodulation are also potential interference mechanisms and have been the underlying issues in several contentious spectrum controversies in the last decade. Realistic receivers have "near/far problems" when the desired signal is much weaker than an adjacent channel signal. These problems most seriously affects mobile receivers since cost, size, and power constraints in mobile units limit the filter performance that is practical to keep adjacent channel signals out of the receiver amplifiers and mixers where strong undesired signals can result in interference.

Measurement and modeling of multiuser multiantenna system in aircraft in the presence of electromagnetic noise and interference

This article evaluates the accuracy with which the performance of a multiuser multiantenna system can be predicted with and without considering cochannel interference and noise (Gaussian, α-stable, and Cauchy) using a site-specific three-dimensional (3D) ray tracing algorithm as well as with statistical models with Gaussian and Nakagami-m channel models in small to medium sized aircraft. These models expand on previous statistical channel models such as the hyper-Rayleigh model by including the simultaneous effects of cochannel and adjacent channel interference, antenna matching, efficiency, directivity and polarization as well as (for the 3D model) site-specific multipath effects. Measurements and comparisons are made in a metallic-bodied Beech Baron BE 58P and a composite structure Rockwell T-39 Sabreliner. It was found that the 3D ray tracing model provides a mean capacity within 1% of those measured in the two aircraft in the presence of interference and noise. This was closely followed by the Nakagami-m distribution (m = 1.4), which was within 1–3% of measured capacity in the presence of interference and within 6% for a combination of interference and noise and the Gaussian model which was within 6% of measured capacity in the presence of interference and within 11% for a combination of interference and noise. The Cauchy noise degraded the capacity more than the other types of noise in the aircraft, providing a lower bound for capacity in an aircraft system. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1137–1144, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25939

Spectrum Sensing for TV White Space in North America

Spectrum sensing for the use of TV spectrum in North America is addressed in this paper. A unified signature-based spectrum sensing algorithm is designed for the primary licensed signals including NTSC analog TV and ATSC digital TV signals. In addition, an autocorrelation-based spectrum sensing algorithm is proposed for the secondary licensed signals such as wireless microphone signals. To our knowledge, the spectrum sensing algorithms presented in this paper are the first one which can reliably determine the availability of a TV channel for unlicensed radio transmissions in the presence of a strong adjacent channel interferer and the target signal strength is as low as -114 dBm.

Otimização do desempenho de amplificadores de radiofrequência banda larga: uma abordagem experimental

Neste trabalho buscou-se avaliar o comportamento de amplificadores de radiofrequência (RF) de potência em aplicações de telecomunicações. Uma estratégia experimental foi empregada resultando na otimização de um conjunto de fatores responsáveis pelo aumento da linearidade e eficiência geral do amplificador durante o processo produtivo, reduzindo com isto as intermodulações geradas e a interferência em serviços adjacentes. Estes resultados permitiram a manufatura de amplificadores banda larga de alta eficiência, garantindo assim maior produtividade e confiabilidade.

Adjacent channel interference in 802.11a is harmful: Testbed validation of a simple quantification model

Wireless LAN radio interfaces based on the IEEE 802.11a standard have lately found widespread use in many wireless applications. A key reason for this was that although the predecessor, IEEE 802.11b/g, had a poor channelization scheme, which resulted in strangling adjacent channel interference (ACI), 802.11a was widely believed to be ACI-free due to a better channelization combined with OFDM transmission. We show that this is not the case. ACI does exist in 802.11a, and we can quantify its magnitude and predict its results. For this, we present minor modifications of a simple model originally introduced by that allow us to calculate bounding values of the 802.11a ACI, which can be used in link budget calculations. Using a laboratory testbed, we verify the estimations of the model, performing experiments designed to isolate the affected 802.11 mechanisms. This isolation was enabled by not using the wireless medium, and emulating it over cables and attenuators. Our results show clear throughput degradation because of ACI in 802.11a, the magnitude of which depends on the interfering data rates, packet sizes, and utilization of the medium.

Development of Multi Channel Ad-Hoc Network System

This paper proposes a new Ad-Hoc network system which comprises the multiple relay access points (APs) with multi channels. Ad-Hoc network systems are recently proposed and incorporated for the communication infrastructure, which relays wireless transmission among access points (APs) in wireless LAN (WLAN) system. System throughput is decreased due to hidden terminal problem when only a single channel is used for the Ad-Hoc network. In order to solve this problem, a new system with multi channels is proposed. However, even if the multi channels are employed, the co- and/or adjacent-channel interference occurs due to hidden terminal problem and multiple APs in a limited space, when considering a simultaneous transmit and reception at the relay AP. In this paper, we develop an Ad-Hoc network testbed which can reduce and avoid co- and/or adjacent-channel interference by using vertically arranged antenna configuration and distributed channel allocation scheme. Moreover, the effectiveness of our testbed is clarified by applying actual WLAN signals.

Pulse Shape Filtering in Wireless Communication-A Critical Analysis

The goal for the Third Generation (3G) of mobile communications system is to seamlessly integrate a wide variety of communication services. The rapidly increasing popularity of mobile radio services has created a series of technological challenges. One of this is the need for power and spectrally efficient modulation schemes to meet the spectral requirements of mobile communications. Pulse shaping plays a crucial role in spectral shaping in the modern wireless communication to reduce the spectral bandwidth. Pulse shaping is a spectral processing technique by which fractional out of band power is reduced for low cost, reliable , power and spectrally efficient mobile radio communication systems. It is clear that the pulse shaping filter not only reduces inter-symbol interference (ISI), but it also reduces adjacent channel interference. The present paper deals with critical analysis of pulse shaping in wireless communication.

Analysis on Characteristics for Sharing Co-channel between Communication Systems

In this paper, we analyze the distance between two systems, WiBro and WLAN, compared to standard interference probability for channel co-use in order to be used as a criteria in realization. Co-channel and adjacent channel interference probability and its effect of (WiBro) into Wireless LAN (WLAN) in TV White Spaces (TVWS) is evaluated through Spectrum Engineering Advanced Monte Carlo Analysis Tool(SEAMCAT) based on the Monte-Carlo simulation method. As a result, in the case of co-channel interference, the minimum distance between WiBro Mobile Station(MS) and WLAN User Equipment (UE) should be 210 m to allow the maximum transmitter power of WiBro UE of 25 dBm. The transmit power of WiBro BS have to be reduced to -4.96 dBm.

A Multiphase Multipath Technique With Digital Phase Shifters for Harmonic Distortion Cancellation

Nonlinearities in transmitter circuits, such as power amplifiers, cause degradation in system performance and adjacent-channel spectral growth interference. Polyphase multipath is considered among the techniques that can compensate the nonlinearities, creating a clean output spectrum. However, the polyphase technique requires analog phase shifters that consume considerable power. Aiming at reducing the power consumption, this brief presents a novel multiphase multipath technique with digital phase shifters. The technique is capable of canceling most of the harmonic and intermodulation products produced by a current-output nonlinear circuit to achieve the required linearity. The proposed system has advantages over existing polyphase techniques in power consumption, accuracy, and flexibility. However, it lacks image rejection and local oscillator harmonic cancellation. Detailed analyses and simulations of the new technique are provided to show the effectiveness of the harmonic distortion cancellation.

Analysis and compensation for nonlinear interference of two high-order modulation carriers over satellite link

We introduce analytical characterization of the nonlinear interference that results when passing more than one high-order modulation carrier through the same nonlinear transponder high-power amplifier (HPA). A Volterra filter is proposed which is novel in its implementation of this analytical characterization and modeling of intersymbol interference (ISI) and adjacent channel interference (ACI). Our focus is on adaptive algorithms with pilot-based training so that the solutions are completely blind to unknown transponder HPA characteristics, and can rapidly respond to varying operating back-off level. Furthermore, two families of adaptive solutions are provided to compensate for nonlinear ISI and ACI. The first set performs adaptive channel inversion and then applies equalization. The second set of solutions performs adaptive channel identification and then applies cancellation. The effectiveness of the proposed analysis and techniques is demonstrated via extensive simulations for high-order QAM and APSK modulations. Also included is the coded performance with selected LDPC codes designed for the DVB-S2 standard. Finally, computational complexity is assessed and performance impact is quantified when complexity is reduced by decreasing the number of Volterra coefficients.

OPTIMUM BLOCK ADAPTIVE ICA FOR SEPARATION OF REAL AND COMPLEX SIGNALS WITH KNOWN SOURCE DISTRIBUTIONS IN DYNAMIC FLAT FADING ENVIRONMENTS

Efficient co-channel and adjacent channel interference rejection is often one of the most demanding requirements for wireless receivers. Independent Component Analysis (ICA) has been previously applied to realize interference suppression. In particular, the fixed-point FastICA and complex FastICA algorithms can successfully perform blind signal extraction for real and complex valued communication signals in stationary or slow fading environments. Both algorithms exhibit fast convergence speed and impressive accuracy due to their Newton type fixed-point iteration. However, under dynamic channel conditions often encountered in practice, the fixed-point algorithms' performance is significantly degraded. In this contribution, a novel complex block adaptive ICA algorithm and its simplified real version is proposed, that overcome this limitation for the separation of complex valued and real signals with known source distributions. The new methods exploit prior information about the modulation scheme of the communication signals of interest, and achieve improved interference suppression performance in dynamic channel environments. The proposed complex ICA algorithm is called Complex Optimum Block Adaptive ICA (Complex OBA-ICA), and its abridged version for separating real signals is called General Optimum Block Adaptation ICA (GOBA-ICA). The proposed methods are applied to interference rejection in linearly and abruptly flat fading dynamic environments for diversity QPSK and BPSK wireless receivers. Simulation results show that the presented techniques demonstrate better convergence properties and accuracy as compared to the complex FastICA and FastICA algorithms.

Error Rate Analysis of Band-Limited BPSK With Nakagami/Nakagami ACI Considering Nonlinear Amplifier and Diversity

An exact expression of the average error rate is developed for a band-limited binary phase-shift keying (BPSK) system in the presence of adjacent channel interference (ACI) considering a Nakagami fading channel. The system employs a root-raised cosine (RRC) filter both in the transmitter and receiver sides and a transmitter power amplifier (PA) that may have nonlinear input/output characteristics. These practical considerations are accurately taken into account. By utilizing the characteristic function (CF) method of error-rate analysis, we interestingly blend the concepts of time and frequency domains and develop an error-rate expression that is simple and general for several system parameters, including adjacent channel separation, RRC filter roll-off factor, and PA output back-off (OBO). Hence, the error rate in the presence of cochannel interference (CCI) is obtained as a special case. The developed results for a single-branch receiver are then extended for diversity receivers, and several interesting observations are made.

분산 중계기 Part 2: 실험실 테스트 결과

본 논문에서는 ATSC (Advanced Television Systems Committee) 지상파 디지털 TV 방송 방식에서의 분산 주파수 망(distributed frequency network)을 위해 개발된 분산중계기(Distributed Translator: DTxR)에 대한 실험실 테스트 결과를 기술하고, 그 결과를 분석한다. DTxR 실험실 테스트는 수신부 테스트와 송신부 테스트로 구분된다. DTxR 수신부 테스트는 dynamic range, 랜덤 잡음, 단일 에코, 인접채널 신호의 간섭 테스트 등을 포함하고, DTxR 송신부 테스트는 출력신호의 품질(대역외 방사, 송신 품질, 위상잡음), 출력신호들의 주파수 일치, TxID (Transmitter Identification) 신호가 상용 수신기에 미치는 영향 평가 등을 포함한다. 실험실 테스트 결과에 의하면, DTxR 수신부는 0~17 us 범위 내의 평균 -2.5 dB의 단일 에코 신호를 제거하며, 랜덤 잡음에 대한 TOV (Threshold of Visibility)는 평균 17.5 dB이다. 또한, DTxR 송신부 출력 신호는 미국의 FCC (Federal Communications Commission) 규격을 만족하며, DTxR 출력신호들의 주파수 차이는 0.001 Hz 보다 작다. This paper presents and analyzes laboratory test results of distributed translator (DTxR) for distributed frequency network (DFN) in the ATSC (Advanced Television Systems Committee) terrestrial digital TV broadcasting system. The DTxR laboratory test is classified to receiving part test and transmitting part test. The receiving part test includes dynamic range, random noise, single echo, and adjacent channel interference. The transmitting part test includes quality of output signal (out-of channel emission, quality of transmitting signal, and phase noise), frequency synchronization among output signals, and TxID (Transmitter Identification) signal's affect to the legacy receiver. By the laboratory test results, the receiving part of DTxR eliminates average -2.5 dB of single echo and has average 17.5 dB at TOV (Threshold of Visibility) under random noise environment. In addition, the transmitting part of DTxR satisfies the specification of US FCC (Federal Communications Commission), and frequency difference among DTxR output signals is less than 0.001 Hz.

Adjacent Channel Interference Reduction for M-WiMAX TDD and WCDMA FDD Coexistence by Utilizing Beamforming in M-WiMAX TDD System

In this paper, we analyze the coexistence issues of M-WiMAX TDD and WCDMA FDD systems. Smart antenna techniques are applied to mitigate the performance loss induced by adjacent channel interference (ACI) in the scenarios where performance is heavily degraded. In addition, an ACI model is proposed to capture the effect of transmit beamforming at the M-WiMAX base station. Furthermore, a MCS-based throughput analysis is proposed, to jointly consider the effects of ACI, system packet error rate requirement, and the available modulation and coding schemes, which is not possible by using the conventional Shannon equation based analysis. From the results, we find that the proposed MCS-based analysis method is quite suitable to analyze the system theoretical throughput in a practical manner.

Improvement on Diversity Gain with Filter Bandwidth Enlargement in Fractional Sampling OFDM Receiver

A diversity scheme with Fractional Sampling (FS) in an OFDM receiver has been investigated recently. Through FS, it is possible to separate multipath components and obtain diversity gain in OFDM systems. Enlargement of the bandwidth of the total frequency response between transmit and receive baseband filters allows the FS scheme to achieve path diversity. However, the transmit filter has to be designed according to the spectrum mask of the wireless standards such as IEEE802.11a/g to avoid interference to the other communication systems and the frequency response of the composite channel including the transmit and receive filters has often been set to minimal bandwidth to eliminate adjacent channel signals. In order to achieve the maximum signal-to-noise ratio (SNR), the same filter is commonly used in the transmitter and the receiver. In this paper, the trade-off among the SNR deterioration, adjacent channel interference, and the diversity gain due to the enlargement of the bandwidth of the receive filter is investigated. Numerical results from computer simulations indicate that the BER performance with wider bandwidth in the receiver shows better performance than that with the minimal bandwidth for maximizing the SNR in certain conditions.

Peak-to-Average Power Reduction of OFDM Signals by Convex Optimization: Experimental Validation and Performance Optimization

We evaluated the application of the convex optimization to peak-to-average power reduction on an orthogonal frequency division multiplexing (OFDM) 802.11a signal. A radio frequency power amplifier was excited with an OFDM signal, and the peak-to-average reduced counterpart and its performance figure of merits were measured and compared. A state-of-the-art radio frequency test system with high accuracy was used for this purpose. Improvements due to the optimization in the output power and power-added efficiency and the influence of the power distribution in the excitation signal on power amplifier performance were investigated. Improvements of 6 dB in output power and 6.5% in power-added efficiency were achieved on average near the operating region. The effect of preserving power-free guard subcarriers was introduced in the optimization algorithm and investigated regarding adjacent channel interference. An improvement of 9 dB from that aspect was observed using half of the power-free subcarriers, which reveals the importance of a guard interval.