IS-95 Code Division Multiple Access Research Articles

Characteristics of GaAs Power MESFETs with Double Silicon Ion Implantations for Wireless Communication Applications

GaAs power metal-semiconductor field-effect transistors (MESFETs) were fabricated using direct double silicon (Si) ion implantation technology for wireless communication applications. A 150-µm MESFET had a saturation drain current of 238 mA/mm after Si3N4passivation. A 15-mm MESFET, when measured under a class-AB condition with a biased drain voltage of 3.4 V and a quiescent drain current of 600 mA, delivered a maximum output power (Pout) of 31.1 dBm and a maximum power-added efficiency (PAE) of 58.0% at a frequency of 1.88 GHz. The MESFET exhibited aPoutof 29.2 dBm with a PAE of 45.0% at the 1-dB gain compression point. The MESFET, when measured under a deep class-B condition with a biased drain voltage of 4.7 V and a quiescent drain current of 50 mA, achieved a maximumPoutof 33.1 dBm and a maximum PAE of 55.9% at 1.88 GHz. The MESFET operating at 4.7 V and 1.88 GHz exhibited aP1dBof 31.8 dBm and an associated PAE of 47.1% at the 1-dB gain compression point. When tested by IS-95 code-division multiple access (CDMA) standard signals and biased at 4.7 V under the deep class-B condition, the MESFET with aPoutof 28 dBm demonstrated an adjacent channel power rejection (ACPR) of –31.2 dBc at +1.25 MHz apart from the 1.88 GHz center frequency and –45.7 dBc at +2.25 MHz.

Low-Cost Design of an FIR Filter by Using a Coefficient Mapping Method

This work presents a novel coefficient mapping method to reduce the area cost of the finite impulse response (FIR) filter design, especially for optimizing its coefficients. Being capable of reducing the area cost and improving the filter performance, the proposed mapping method consists of four steps: quantization of coefficients, import of parameters, constitution of prime coefficients with parameters, and constitution of residual coefficients with prime coefficients. Effectiveness of the proposed coefficient mapping method is verified by selecting the 48-tap filter of IS-95 code division multiple access (CDMA) standard as the benchmark. Experimental results indicate that the proposed design with canonical signed digit (CSD) coefficients can operate at 86 MHz with an area of 241,813 um2, leading to a throughput rate of 1,382 Mbps. Its ratio of throughput/area is 5,715 Kbps/um2, yielding a higher performance than that of previous designs. In summary, the proposed design reduces 5.7% of the total filter area, shortens 25.7% of the critical path delay, and improves 14.8% of the throughput/area by a value over that of the best design reported before.

A Watt-Level Stacked-FET Linear Power Amplifier in Silicon-on-Insulator CMOS

A single-stage stacked field-effect transistor (FET) linear power amplifier (PA) is demonstrated using 0.28-?m 2.5-V standard I/O FETs in a 0.13-?m silicon-on-insulator (SOI) CMOS technology. To overcome the low breakdown voltage limit of MOSFETs, a stacked-FET structure is employed, where four transistors are connected in series so that their output voltage swings are added in phase. With a 6.5-V supply, the measured PA achieves a small-signal gain of 14.6 dB, a saturated output power of 32.4 dBm, and a maximum power-added efficiency (PAE) of 47% at 1.9 GHz. Using a reverse-link IS-95 code division multiple access modulated signal, the PA shows an average output power of up to 28.7 dBm with a PAE of 41.2% while meeting the adjacent channel power ratio requirement. Using an uplink wideband code division multiple access modulated signal, the PA shows an average output power of up to 29.4 dBm with a PAE of 41.4% while meeting the adjacent channel leakage ratio requirement. The stacked-FET PA is designed to withstand up to 9 V of supply voltage before reaching its breakdown limit. This is the first reported stacked-FET linear PA in submicrometer SOI CMOS technology that delivers watt-level output power in the gigahertz frequency range with efficiency and linearity performance comparable to those of GaAs-based PAs.

A 20 dBm Linear RF Power Amplifier Using Stacked Silicon-on-Sapphire MOSFETs

In this letter, a fully integrated 20-dBm RF power amplifier (PA) is presented using 0.25-mum-gate silicon-on-sapphire metal-oxide-semiconductor field-effect transistors (MOSFETs). To overcome the low breakdown voltage limit of MOSFETs, a stacked FET structure is employed, where transistors are connected in series so that each output voltage swing is added in phase. By using triple-stacked FETs, the optimum load impedance for a 20-dBm PA increases to 50Omega, which is nine times higher than that of parallel FET topology for the same output power. Measurement of a single-stage linear PA shows small-signal gain of 17.1 dB and saturated output power of 21.0dBm with power added efficiency (PAE) of 44.0% at 1.88 GHz. With an IS-95 code division multiple access modulated signal, the PA shows an average output power of 16.3 dBm and PAE of 18.7% with adjacent channel power ratio below -42dBc

A blind coherent spatiotemporal processor of orthogonal Walsh‐modulated CDMA signals

AbstractA more efficient detection of orthogonal Walsh‐modulated Code Division Multiple Access (CDMA) signals is required not only for better exploitation of current IS‐95 CDMA systems but also for future cdma2000 3G networks. Integration of adaptive antennas at the base station has been recognized as one key lever to increasing capacity and spectrum efficiency. Prospective array‐receiver solutions such as the 2‐D‐RAKE improve performance; however, in the absence of a pilot signal, they have to implement noncoherent detection. In this work, we propose a space‐time processor that achieves coherent detection of orthogonal Walsh‐modulated CDMA signals without a pilot. We assess its performance in spatially correlated Rayleigh‐fading. Simulation results for voice links of 9.6 Kbps indicate that up to an antenna‐correlation factor of 0.8, the proposed receiver outperforms the conventional 2‐D‐RAKE's capacity by 90% in nonselective fading. This gain shrinks fast at higher correlation factors. In selective fading, however, it maintains about a 130% gain in capacity over the entire correlation range. For data links of 153.6 Kbps, this performance advantage increases up to 180–200%. With high‐speed mobiles, however, it vanishes quickly at correlation factors beyond 0.5. Overall, the capacity gains of the proposed spatiotemporal receiver structure increase with reduced relative Doppler (Doppler‐frequency/symbol‐rate ratio). This may arise from increased spatiotemporal diversity, higher transmission rates, and/or slower mobility. Copyright © 2002 John Wiley & Sons, Ltd.

Wireless voice-over-IP and implications for third-generation network design

The recent rise of voice-over-Internet protocol (IP) as an alternative to circuit-based telephony poses some serious questions to the wireless community. Will wireless voice-over-IP and multimedia-over-IP gain momentum over their circuit-based alternatives? Should the design of third-generation (3G) wireless systems take these alternatives into account? In this paper we describe two models of wireless voice-over-IP and discuss additional requirements necessary to support business-grade-quality voice in the face of mobility. The case studies we present assumed an air interface of IS-95 code division multiple access (CDMA) or IS-136 time division multiple access (TDMA). The results of our studies show that business-grade voice-over-IP may not be economical for the licensed cellular and personal communications services (PCS) radio spectrum because the cost of licensing the cellular/PCS radio spectrum is high and the circuit-mode air interface is already efficient. To compete in various markets, however, 3G networks should efficiently support both wireless voice-over-IP and multimedia-over-IP. To do this, 3G networks should meet the challenge of seamless packet data handoffs and deep compression of user data protocol (UDP)/IP headers. Efficient support for wireless multimedia-over-IP may be even more critical (compared to voice-over-IP) for helping packet-based 3G multimedia such as H.323 to compete with its broadband integrated services digital network (B-ISDN) counterpart. As wireless voice and data converge in the 3G world, betting on packet-data mobility in addition to voice mobility may be a key to enabling the wireless industry to fuel the explosive growth of mobile subscribers worldwide.

A new block interleaver and noniterative decision feedback decoding enhance performance of IS-95 CDMA uplink or similar M-ary system

This paper investigates the combination of a new block interleaver design and a noniterative decision feedback receiver/decoder for IS-95 code-division multiple-access (CDMA) uplink in additive white Gaussian noise and a Rayleigh fading multipath environment. The new interleaver design yields better performance than the currently used IS-95 interleaver, with E/sub b//N/sub 0/ improvements of 0.27 to 0.76 dB. At the same time, the new interleaver design improves the effectiveness of a noniterative decision feedback receiver/decoder herein presented. The performance of the proposed design is measured via computer simulation for both coherent and noncoherent detection. A mathematical justification is also given to show the reason why the performance is improved using the proposed design. Based on these results, it is concluded that the use of the new interleaver design with noniterative decision feedback decoding can improve the quality of service and/or capacity of a modified cellular IS-95 system or a system using a similar concatenation of convolutional coding, interleaving, and orthogonal Walsh modulation. Although the approach presented is applied to the uplink of IS-95, it can also be applied to similar M-ary systems.

A linearized power method for adaptive beamforming in a multipath fading CDMA environment

AbstractThis paper discusses an adaptive procedure of a simplified power method for computing the eigenvector corresponding to the largest eigenvalue of an autocovariance matrix. The objective is to generate a suboptimal weight vector for an adaptive array operating in a multipath fading CDMA (code‐division multiple access) channel. The total computational load of the proposed procedure is about O(4N), including an autocovariance matrix update, where N is the number of weights. The performance of the proposed array system is shown in terms of the BER (bit‐error rate) and the allowable capacity in a modeled IS‐95 CDMA signal environment. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 361–365, 2001.

Analysis of peak-to-average power ratio for IS-95 and third generation CDMA forward link waveforms

The peak-to-average power ratio (PAR) of IS-95-type code division multiple-access (CDMA) forward link waveforms is an important parameter which directly relates to system capacity performance. In this paper, analytical expressions are derived for the PAR. The probability that the instantaneous-to-average power ratio (IAR) exceeds a given value is also derived. The analysis is carried out parametric in 1) the number of active traffic channels; 2) the fractions of power allocated to different forward link channels; and 3) other parameters related to the forward link power budget. An analysis is also given for the distribution of the IAR for the forward link modulation planned for third generation (3G) versions of the IS-95 system and a simple modification to present and future IS-95 modulation schemes is shown that reduces the forward link PAR by up to 3 dB.

Performance Improvement of IS-95 CDMA Uplink Using Decision Feedback and Sub-Optimal Viterbi Decoding

This paper presents a methodology designed to improve the effectiveness of a non-iterative decision feedback (DF) receiver/decoder for IS-95 Code Division Multiple Access (CDMA) uplink in additive white Gaussian noise (AWGN) and Rayleigh fading. The effectiveness of the DF receiver/decoder is linked to the interleaver specification and the decoding delay of the convolutional decoder. Using sub-optimal convolutional decoding the average decoding delay is reduced resulting in more effective decision feedback decoding (DFD). Simulation results of average decoding delay, bit error rate (BER) and frame error rate (FER) are presented for coherent and noncoherent detection of unfaded single-path and Rayleigh fading multipath signals. Instead of the usual performance degradation these results show that the DF receiver/decoder benefits from some forms of sub-optimal Viterbi decoding. The additional performance gain can further improve the quality of service and/or capacity of a cellular IS-95 system.

A GaAs/AlAs Wet Selective Etch Process for the Gate Recess of GaAs Power Metal-Semiconductor Field-Effect Transistors

A highly selective wet chemical etch process for gate recess of the GaAs power metal-semiconductor field effect transistors (MESFETs) was developed. The power MESFETs used in this study were epitaxially grown devices with a 20 Å AlAs etch-stop layer for gate recess. The selective etch process using citric acid/potassium citrate/hydrogen peroxide solution was studied. A selectivity better than 3800:1 was achieved for GaAs/AlAs layers. This selective etch was applied both to high-power, high-voltage power MESFETs and low-voltage large-periphery power MESFETs. For high-power applications, the 14.7 mm device had a breakdown voltage of 22 V. When tested at 1.88 GHz with a drain bias of 10 V, it provided a maximum output power of 38.8 dBm and a maximum power-added efficiency of 52.5%. For low-voltage applications, the 19.8 mm device was tested under IS-95 code-division multiple access (CDMA) modulation at 1.88 GHz with a drain bias of 3.5 V. Under CDMA modulation, the device showed an output power of 28.03 dBm with an adjacent channel power rejection of −29.6 dBc at 1.25 MHz offset frequency. Both devices also showed excellent uniformity in pinch-off voltages. © 2000 The Electrochemical Society. All rights reserved.

Computationally efficient smart antennas for CDMA wireless communications

The analysis in this paper concerns the performance of smart antenna algorithms when used in code-division multiple access (CDMA) wireless communication systems. Complex pseudonoise (PN) spreading, despreading, and pilot-aided channel estimates in the cdma2000 reverse link are some of major characteristics that are different from those in the IS-95 CDMA systems. These different features are included in our analysis. Four computationally efficient smart antenna algorithms are introduced: 1) smart antenna based on maximum output power criteria without Lagrange multiplier; 2) smart antenna based on maximum signal-to-interference-plus-noise output power ratio (SINR) criteria with eigenvector solution; 3) smart antenna based on maximum SINR output criteria without eigenvector solution; 4) more simplified smart antenna based on maximum SINR output criteria without eigenvector solution. Algorithms (1) and (4) require only 4M computational instruction cycles per snapshot where M is the number of antenna array elements. Algorithms (2) and (3) require M/sup 2/ and (4M+2M/sup 2/) operations per snapshot, respectively. These computational loads are significantly smaller than those of typical eigenvalue decomposition blind detection approaches. Bit error rates (BERs) resulting from these algorithms are evaluated through simulation. A double spike power delay profile with equal or unequal power is used. Also, a cluster of interfering users and scattered interference users are considered. For BER comparisons, antenna diversity using equal gain combining is also analyzed. The four smart antenna algorithms show significant capacity improvement compared to the antenna array diversity using equal gain combining under the double spike power delay profile with equal power and scattered interference environments.

A planar gate double beryllium implanted GaAs power MESFET for low voltage digital wireless communication application

An ion-implanted planar gate power MESFET for low voltage digital wireless communication system including DCS1800 (digital cellular system at 1800 MHz) and CDMA (code division multiple access) handset applications has been developed. The process for the device developed contains double Be implantation to reduce the surface and substrate defect trapping effects. The MESFET process developed has very little gate recess (less then 200 /spl Aring/), which greatly improves the uniformity and the yield of the wafer. The 1 /spl mu/m/spl times/20 mm MESFET manufactured using this planar gate technology exhibits an output power of 32.98 dBm and power added efficiency over 53% with gain of 11.2 dB when tested at 1.9 GHz under 3.6 V drain bias voltage and 80 mA quiescent drain current. The pinch off voltage of the 20 mm devices within a wafer is -2.81 V with a standard deviation of 120 mV. The device was also tested at 3.6 V and 1.9 GHz for CDMA application. Under the IS-95 CDMA modulation at 28 dBm output power, the device gain is 10.7 dB and the device has an adjacent channel power rejection (ACPR) of -29.5 dBc at 1.25 MHz offset frequency and -44.9 dBc at 2.25 MHz offset. The test data shows that the double Be implanted devices developed using the planar gate technology have very good linearity and efficiency and can be used for the low voltage DCS1800 and CDMA handset applications.

Efficient video transmission over correlated Nakagami fading channels for IS-95 CDMA systems

This paper deals with the problem of efficient transmission of video signals over generalized fading channels in direct sequence-spread spectrum (DS-SS) code division multiple access (CDMA) systems. We first propose a modified version of the H.263 video codec incorporating a selective forward error correction (FEC) coding scheme combined with a forced intra-frame update mechanism. The modified codec results in the improvement of the average video and frame-to-frame performance. We further consider a coherent DS-CDMA system for the forward link (base-to-mobile) in both single-cell and multiple-cell environment. We provide performance evaluation results by both analysis, employing the Gaussian approximation, and computer simulations, using Monte Carlo error counting techniques. By integrating the proposed video codec with a coherent DS-CDMA system based upon the IS-95 standard, we investigate the performance of the video transmission over frequency-selective, correlated Nakagami fading forward-link channels employing a RAKE receiver. To simulate the fading channel, we have implemented in software a correlated Nakagami fading simulator based upon the principle of superposition of complex partial waves, an approach which replicates the wave propagation process in actual physical situations. A variety of performance evaluation results, both in single-cell and multiple-cell environment, are presented for a different number of resolving paths, cell user capacity, signal propagation characteristics, as well as for the presence of channel estimation errors. Heuristic explanations and interpretations of the trend of the obtained results are also given.

Power PHEMT with compact device layout for low voltage CDMA application

A high efficiency low voltage operation dual delta-doped AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) for low voltage code division multiple access (CDMA) application has been developed. When tested at 2.4 V and 1.9 GHz under IS-95 CDMA modulation, the 20.16 mm PHEMT device was found to have a linear output power of 28 dBm with a power added efficiency of 30.2%. The device also has a saturation power of 30.0 dBm with a power added efficiency of 61.5%. The high efficiency and linearity of the PHEMT at low bias voltage is attributed to the use of the dual delta-doped PHEMT structure and to the reduction of the size of the device layout. The device is suitable for low voltage CDMA applications.

The feasibility study of transporting IS-95 CDMA signals over HFC networks

This letter studies the feasibility of transmitting IS-95 code-division multiple-access (CDMA) wireless signals in hybrid-fiber-coax (HFC) networks. Capacity estimation of an HFC optical node-based CDMA cellular systems using a return-path channel model is provided. In addition to multiple-access interference in IS-95 CDMA networks, the return-path channel model takes into account ingress noise, impulsive noise, and microreflections in a coaxial cable transmission system; and laser diode clipping-induced intermodulation noise in an optical fiber link.

Complementary filter design for testing of IS-95 code division multiple access wireless communication systems

In this paper, a simple design of a complementary filter is presented for performance measurement of an IS-95 code division multiple access wireless communication system (1995). The complementary filter is required to meet the design requirements, which are specified in IS-97 document (1994). The purpose of employing the complementary filter in test equipment is to remove intersymbol interference introduced by the base station transmit-filter and the transmit-phase equalizer. Five window functions, which do not affect the desirable response at the proper sampling times, are applied to the desirable output. The output of a window Is set to be the output of the complementary filter. Then, the complementary filter is obtained by taking a deconvolution of the output response of the window with the impulse response resulted by cascading the base station transmit-filter and the transmit-equalizer. It is found that the output of the complementary filter with the Kaiser window function meets all requirements specified in IS-97. In addition, it is observed that the Kaiser window has the smallest number of the filter coefficients among all windows considered in this paper. Therefore, the complementary filter with the Kaiser window is recommended for implementation of the IS-95 system measurement.

A Decision Feedback Reverse Link Receiver Implementation for IS-95 CDMA Communications

An implementation of a reverse link receiver for IS-95 CDMA (Code-Division Multiple-Access) communications that applies decision feedback to the decoding of the received signal is presented. Decision feedback is used in order to improve BER performance by making use of additional information that conventional receiver designs generally ignore. Qualitative analysis and computer simulation of the hardware components of the proposed implementation shows that it can be built as a single integrated circuit using present day technology. The design presented here does not include the RF front-end of the receiver, does not consider the effects of multipath and fading on system performance, and assumes perfect power control.

Combined source-channel coding for the transmission of still images over a code division multiple access (CDMA) channel

This letter considers a combined source-channel coding scheme for image transmission over the uplink of a wireless IS-95 code division multiple access (CDMA) channel using discrete cosine transform. By adjusting the dimension of the orthogonal signaling scheme, we trade the system error-correction capability for a faster bit rate. The increase in channel error is relieved by employing a set of quantizers which are designed using a joint source-channel optimization algorithm.

Soft handoffs in CDMA mobile systems

This article presents an overview of soft handoff, an idea which is becoming quite important because of its use in the IS-95 code-division multiple access (CDMA) cellular phone standard. The benefits and disadvantages of using soft handoff over hard handoff are discussed, with most results drawn from the available literature. The two most well-known benefits are fade margin improvement and higher uplink capacity, while disadvantages include increased downlink interference and more complex implementation. Handoff parameter optimization is extremely important, so various studies on the trade-offs to be considered when selecting these parameters are surveyed, from both the link quality and resource allocation perspectives. Finally, research directions and future trends are discussed.