Performance analysis of reverse link wideband CDMA cellular system under fast closed-loop power

We evaluate the capacity and bandwidth efficiency of microcellular CDMA systems. Power control, multipath diversity system bandwidth, and path loss exponent are seen to have a major impact on the capacity. The CDMA system considered uses convolutional codes, orthogonal signalling, multipath/antenna diversity with noncoherent combining, and fast closed-loop power control on the uplink (portable-to-base) direction. On the downlink (base-to-portable), convolutional codes, BPSK modulation with pilot-signal-assisted coherent reception, and multipath diversity are employed. Both fast and slow power control are considered for the downlink. The capacity of the CDMA system is evaluated in a multicell environment taking into account shadow fading, path loss, fast fading, and closed-loop power control. Fast power control on the downlink increases the capacity significantly. Capacity is also significantly impacted by the path loss exponent. Narrowband CDMA (system bandwidth of 1.25 MHz) requires artificial multipath generation on the downlink to achieve adequate capacity. For smaller path loss exponents, which are more likely in microcellular environments, artificial multipath diversity of an order of as high as 4 may be needed. Wideband CDMA systems (10 MHz bandwidth) achieve greater efficiencies in terms of capacity per MHz. >

The benefits of employing antenna array processing for the interference limited UMTS system is the increase in the number of simultaneous users and the reduction in the transmitted uplink power. The joint power control and antenna processing offers maximum achievable capacity with lower transmission powers for the given target SINR (signal-to-interference+noise ratio). The analysis about possible achievements using antenna array processing, varying parameters such as the number of users in a microcell, processing gain and antenna array size for the given target SINR, has been done using a deterministic ray tracing model developed for urban microcells and considering two antenna processing cases, OC (optimum combining) and MRC (maximum ratio combining). The paper shows that the ratio between the target value and the processing gain is the most dominant factor for the antenna array performance in the power controlled environment, and that optimum transmitted powers obtained using OC are the least sensitive to the increase in the number of users, as compared to MRC and simple decorrelation on a single antenna element.

An efficient network is critical to support the rapid growth in traffic on mobile networks, since current network PCS1900 (2G) cannot support such a huge demand. The objective of the third-generation (3G) UMTS (Universal Mobile Telecommunication System) of wireless communication is to provide high speed wireless communication to support multimedia, large data, and video. However, the co-existence of the two mobile radio systems (PCS1900 and UMTS) which share the same frequency band leads to a major issue. A serious issue of co-existence occurs when the downlink of the system is closer to the frequency bands of the concerned system. The PCS-1900 downlink band (1,930-1,990) and WCDMA (UMTS) uplink band (1,920-1,980) widely overlap, which causes interference between UMTS mobile unit and PCS-1900 base station. Therefore the objectives of this paper is to study the effect from PCS 1900 base station interference on UMTS mobile unit performance in terms of the probability of bit error by developing the Probability of bit error equation of DSS-QPSK from the existing Probability of bit error equation. This paper also evaluates the degradation of UMTS mobile unit performance in terms of probability of bit error when the system is interfered by PCS1900 base station.

State of the art high-current superconducting accelerators require efficient RF sources with a fast dynamic phase and power control. This allows for compensation of the phase and amplitude deviations of the accelerating voltage in the Superconducting RF (SRF) cavities caused by microphonics, etc. Efficient magnetron transmitters with fast phase and power control are attractive RF sources for this application. They are more cost effective than traditional RF sources such as klystrons, IOTs and solid-state amplifiers used with large scale accelerator projects. However, unlike traditional RF sources, controlled magnetrons operate as forced oscillators. Study of the impact of the controlling signal on magnetron stability, noise and efficiency is therefore important. This paper discusses experiments with 2.45 GHz, 1 kW tubes and verifies our analytical model which is based on the charge drift approximation.

CDMA is interference limited multiple access system. Power control is an effective way to reduce co-channel interference. Consequently, it can improve the system capacity. CDMA employs fast closed-loop power control in uplink in which signal-to-interference ratio (SIR) is estimated. Transmitting power is adjusted by comparing estimated SIR with desired SIR. In this paper a modified fixed step power control algorithm has been proposed, which can improve the performance of a CDMA system. The proposed algorithm produced a faster convergence and low outage probability compared to other power control algorithms discussed and analyzed to maintain the desired SIR target.

Cooperative sensing (CS) is important for efficiently acquiring spectrum awareness in cognitive radio systems. The main focus of this paper is on the BEP (bit error probability) walls for soft decision (SD) based CS in cognitive radios. The BEP wall is a performance limitation for CS caused by imperfect reporting channels. In this paper, a distributed detection system using parallel sensing topology and a fusion center (FC) is considered. Each secondary user (SU) sends energy-based multibit SD to the FC over a reporting channel with a certain BEP. The maximum output entropy (MOE) quantization is considered for quantizing the estimated energy. For the considered case, it is established that the BEP wall values for SD based CS with MOE quantization are identical for arbitrary number of bits for quantization. Moreover, the BEP wall values for SD based CS with MOE quantization are proven to be the same as the BEP wall values for the Chair-Varshney fusion rule, which is an optimal fusion rule for one-bit hard decision based CS. Later relation between the BEP wall values of the SD based CS and the K-out-of-N fusion rules is also established.

In this article, the performance of M-ary phase shift keying (PSK) modulation schemes over mobile-to-mobile (M2M) fading channels with equal gain combining (EGC) in cooperative networks is analyzed. Narrowband M2M fading channels under line-of-sight (LOS) propagation conditions are modeled as double Rice processes. A dual-hop amplify-and-forward relay network, where LOS components can exist in the transmission links between the source mobile station and the destination mobile station via K mobile relays, is studied. Here, the average bit error probability (BEP) is utilized to evaluate the performance of Mary PSK modulation schemes. A simple analytical approximation for the average BEP of M-ary PSK modulations over relay-based M2M fading channels with EGC is derived. The accuracy of the approximation is assessed by simulations. The presented results show that in a dual-hop relay system with EGC, the presence of LOS components in the relay links improves the systems' performance. In addition, a significant enhancement in the diversity gain can be achieved as the number of diversity branches K increases.

The reverse link performance of direct sequence code division multiple access (DS-CDMA) system in wireless communication over a frequency selective multipath fading channel has been investigated in this paper. The channel has been modeled as Nakagami-m distributed frequency selective multipath fading channel. A conventional correlator type receiver has been considered for the analysis. Noise is taken as additive white Gaussian noise (AWGN) with two sided power spectral density N/sub 0//2 . To model multiple access interference (MAI), standard Gaussian approximation (SGA) has been considered in this paper. To mitigate the near-far problem, a power control scheme, but imperfect has been assumed in this paper. The bit error rate (BER) expression for the system has been derived and simulated by varying number of users, number of fading path, processing gain, fading parameter, SNR per bit E/sub b//N/sub 0/ and variation in the amplitude of the received signal. The analysis shows that as the number of simultaneous active user, the number of fading path and the variation in the power of the received signal increases, the BER of the system increases indicating the performance degradation. As the value of the processing gain, the ratio E/sub b//N/sub 0/ and the fading parameter increases, the BER performance of the system improves.

In an LEO satellite CDMA system, power control can only be used to combat long-term signal loss due to long round trip delay, which calls for different considerations on power control algorithms. Based on the criteria of fast response, small overcompensation, oscillation-avoiding, and minimum power control error, the behavior of the transient response of fixed step power control, adaptive power control, and multistep power control are investigated and compared. A new multistep power control algorithm is proposed for LEO satellite communication systems suffering from high variation in the envelope of the received signal, i.e., high dynamics in slow fading.

기존의 웨이브릿 편이 변조 시스템은 스케일링 함수(scaling function)를 1로, 웨이브릿(wavelet)을 0으로 하는 1비트 변조방법이 있고, 스케일링 함수와 웨이브릿 그리고 이 두 신호를 반전시켜서 생성된 4개의 반송파를 사용하는 2비트 변조방법이 있다. 본 논문에서는 2비트 변조방법인 4-ary 스케일링 웨이브릿 편이변조(4-ary SWSK : 4-ary scaling wavelet shift keying) 시스템을 정의하고, QPSK 시스템으로부터 정의된 시스템의 비트 에러 확률과 부호 에러 확률을 유도한다. 제안한 4-ary SWSK 성능을 분석하기 위하여, 기존의 QPSK(quadrature phase shift keying), MFSK(M-ary frequency shift keying), 그리고 제안한 방법의 비트 에러 확률 및 부호 에러 확률을 구한다. 실험결과 제안한 방법의 비트 에러 확률과 부호 에러 확률이 좋은 성능을 보였다. An algorithm of the conventional wavelet shift keying is carried out that the scaling function and wavelet are encoded to 1(mark) and 0(space) for the input binary data, respectively. Two bit modulation technique which uses four carrier frequencies is existed. Four carrier frequencies are defined as scaling function, inversed scaling function, wavelet, and inversed wavelet, which are encoded to 10, 11, 00 and 01, respectively. In this paper, we defined 4-ary SWSK (4-ary scaling wavelet shift keying) which is two bit modulation, and it is derived to the probability of bit error and symbol error of the defined system from QPSK. In order to analyze to the performance of 4-ary SWSK, we are obtained in terms of the probability of bit error and symbol error for QPSK (quadrature phase shift keying), MFSK(M-ary frequency shift keying) and proposed method. As a results of simulation, we confirmed that the proposed method was superior to the performance in terms of the probability of bit error and symbol error.

This paper explains a robust adaptive coding scheme (CS) based on hybrid error control which is a combination of Forward Error Control (FEC) and Automatic Repeat Query (ARQ) to maximize the throughput and ensure error free data transmission. The system characteristics are suited for wireless application within VHF and HF spectrum. The system design utilizes block code FEC instead of convolution code since it can perform link quality analysis (LQA) without overhead data. The analysis of system performance is made in the presence of combine additive white Gaussian noise (AWGN) and flat fading conditions. Criteria performances are bit-error rate (BER), packet-error rate (PER) and the throughput with a given Signal-to-Noise Ratio (SNR). In addition, a performance comparison with nonadaptive hybrid error control is made.

The subset-based coherent fast frequency hopping (S-CFFH), was recently proposed to enable reliable channel estimation and coherent schemes for FFH over fading channels. In this paper, we analyze the maximum-likelihood (ML) receiver for the S-CFFH/binary phase shift keying (BPSK), with partial band noise jamming (PBNJ), frequency selective Rayleigh fading, and imperfect channel state information (CSI). The expressions of closed-form bit error ratio (BER) are presented, and the results are validated by simulations. It is shown that the proposed ML receiver significantly outperforms some conventional diversity combining receivers in terms of BER. The ML receiver also greatly reduces the jammer's efficiency.

An analytical derivation of the probability of bit error noncoherent frequency-shift keying (FSK) and coherent phase-shift keying (PSK) signals transmitted through a land-mobile satellite channel is described. The channel characteristics used in the analysis are based on a recently developed model which includes the combined effects of fading and shadowing. Analytical expressions for the probability of bit error of FSK and coherent phase-shift keying (CPSK) signals are obtained. The results show that large amounts of signal-to-noise ratio (SNR) are required to compensate for the combined effect of fading and shadowing. An analytical expression for the irreducible probability of bit error of a CPSK signal due to phase variations caused by fading and shadowing is derived. The results described should be useful in the design of land mobile satellite communication systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In the article, a new topical scientific task is solved regarding the assessment of the impact of the error of the synchronization system of the coherent demodulator on the immunity of signals with multi-position phase manipulation. The probability of a bit error is proposed in the article as a criterion for evaluating the immunity of coherent reception of signals with multi-position phase modulation in the presence of a phase error. A model for evaluating the effect of the error of the coherent demodulator synchronization system on the bit error probabilities of signals with multi-position phase manipulation is developed and presented. The presented model is based on the probabilistic characteristics of the appearance of a bit error of a signal with multi-positional phase modulation relative to the accepted level of the phase error of the coherent demodulator at different values of the signal-to-noise ratio at the input of the coherent receiver for signals with different positions. The results of the evaluation of the probability characteristics of the appearance of a bit error in a signal with multi-positional phase modulation in the presence of a phase error of a coherent demodulator showed that with an increase in the positionality of the BFM signal, the influence of static and random errors of the synchronization system on the probability of bit errors increases. At large signal-to-noise ratios, a small phase estimation error, from π/180 to π/90, leads to a significant increase in the probability of bit errors. With random phase fluctuations for signals with M ≥ 4, when the variance Dϕ changes from 0 to 0.01, the error probability can be changed by one or two orders of magnitude. The obtained results allow us to come to the conclusion that during the reception of BFM signals, the permissible value of the carrier phase estimation error depends on the positionality of M and varies from π/36 – π/72 for 2-FM to π/180 for 32-FM.

Adaptive modulation and coding (AMC), power control (PC) and automatic repeat request protocols (ARQ) represent very important link adaptation (LA) techniques for future generations of wireless communication systems. In order to improve the efficiency of these systems, some combination schemes of these LA techniques have been proposed in the literature. Most of these schemes were interested in the combination of only two among the three LA techniques. We have proposed in [8] a novel combination scheme where all of the three LA techniques were optimally combined. The optimality criterion was the maximization of the average throughput efficiency, while meeting an average transmit power constraint, in order to reduce multiple access interference. QoS-sensitive services, like video streaming and IP voice, require a QoS constraint or, equivalently, a packet error probability (PEP) constraint. In this paper we are interested in the optimal combination of the three LA techniques, while satisfying a required PEP performance. More specifically, we derive the optimal AM switching thresholds as well as the optimal transmit power level, in order to achieve the highest average throughput efficiency, given the fading channel conditions and the required error performance. To assess the offered performance gain, the proposed LA scheme is compared to conventional scheme using exclusively AM in combination with ARQ without guaranteeing any QoS. Numerical and simulation results show significant average transmit power gains, with respect to AM-ARQ scheme, while still guaranteeing a satisfying error performance.