Orthogonal frequency-division multiplexing (OFDM) has gained a great deal of attention lately and is considered as a strong candidate for many next-generation wireless communication systems. However, OFDM (in its current implementation) does not demonstrate robustness to narrowband interference. In our earlier work, we showed how carrier interferometry (CI) spreading codes may be applied to spread OFDM symbols over all N subcarriers - this allows OFDM to exploit frequency diversity and improve performance (without loss in throughput). In this paper, we show that, by spreading OFDM symbols over all N subcarriers via CI spreading codes, the resulting carrier interferometry OFDM (CI/OFDM) system is also capable of suppressing narrowband interference. Simulation results for OFDM, coded OFDM (COFDM), CI/OFDM, and coded CI/OFDM over additive white Gaussian noise and multipath fading channels confirm CI/OFDM's robustness to narrowband interference.

OFDM (orthogonal frequency division multiplexing) has gained a great deal of attention of late and is considered a strong candidate for many next generation wireless communication systems. However, OFDM (in its current implementation) does not demonstrate robustness to narrowband interference. In our earlier work, we showed how carrier interferometry (CI) spreading codes may be applied to spread OFDM symbols over all N subcarriers. This allows OFDM to exploit frequency diversity and improve performance (without loss in throughput). In this paper, we show that, by spreading OFDM symbols over all N subcarriers via CI spreading codes, the resulting CI/OFDM system is also capable of suppressing narrowband interference. Simulation results over AWGN and multi-path fading channels confirm CI/OFDM's robustness in the presence of narrowband interference.

DS-CDMA is a dominant player in the world of wireless telecommunications, emerging as the standard of choice in 3G UMTS (Universal mobile telecommunications system). Here, DS-CDMA is also referred to as WCDMA (wideband CDMA). In this work, we introduce a novel multicarrier chip-shaping filter at the transmitter, replacing the usual root-raised cosine chip shape filter in WCDMA systems. At the receiver side, a corresponding frequency-based processing is proposed, where chips are separated into their N carrier components, and then recombined in order to minimize interference and noise while exploiting frequency diversity gains. Our performance analysis assumes system parameters and channel models consistent with UMTS WCDMA standards, and results show that the frequency-based WCDMA physical layer offers a 5 dB-performance gain at P(/spl epsiv/)=10/sup -2/ (uncoded transmission) over a traditional time-based WCDMA system with RAKE reception.

In this work, we propose a new multicarrier platform to optimize the efficiency of wireless operators' licensed bands and to enable flexible sharing of licensed and unlicensed bands (in different spectral regions). This research supports a recent FCC proposal which suggests innovative spectrum management regulations to improve spectral efficiency. Specifically, this work presents a multicarrier platform capable of (1) achieving high spectral efficiency by application of "narrow" orthogonal carriers; and (2) enables flexible spectral sharing across different licensed and unlicensed bands via operator borrowing/ lending.

In traditional binary frequency-shift keying (BFSK), two distinct carrier frequencies are used to represent binary data. In this letter, we propose transmitting multiple orthogonal, in-phase subcarriers around two distinct carrier frequencies to represent binary information. The envelope of the resulting FSK signal is a carrier interferometry pattern, and hence, the name carrier interferometry (CI/) FSK. We demonstrate that this technique is spectrally efficient when compared to traditional BFSK. Performance and data-rate benefits are also demonstrated with the use of a novel coherent reception technique. Moreover, while it is difficult to employ traditional BFSK in multipath channels, we show how the new CI/FSK scheme exploits frequency-diversity benefits when used in such channels.

In this letter, a large set of spreading codes that doubles capacity in multicarrier code-division multiple-access (MC-CDMA) systems without any cost in bandwidth and with negligible cost in performance is introduced. This large set is comprised of: 1) complex spreading codes instead of conventional real-valued spreading codes and 2) two sets, each made up of orthogonal complex spreading codes, with minimum cross correlation between sets. Simulations performed over Rayleigh fading channels demonstrate 100% gains in terms of MC-CDMA capacity with negligible loss in performance.

In this paper, a novel merger of multicarrier code-division multiple access (MC-CDMA) and smart antenna arrays is introduced. Here, a group of Q carriers in the MC-CDMA system is applied to its own M-element smart antenna array at the base station (BS). The smart antennas are located in close proximity to one another. We generate a transmit diversity gain at the receiver by carefully moving (oscillating) the antenna array's pattern. The pattern oscillation is achieved by applying appropriate time-varying phases to array elements of each smart antenna. The beam pattern oscillation ensures a mainlobe at the position of the intended user and small oscillations in the beam pattern. This beam pattern oscillation leads to a time-varying channel with a controllable coherence time; hence, a transmit diversity benefit, in the form of a time diversity benefit, is available at the receiver. Employing MC-CDMA with the proposed smart antenna at the BS, we achieve: 1) directionality which creates high network capacity via space-division multiple access; 2) a transmit diversity gain which supports high performance at the receiver in the mobile unit; and 3) increased capacity and performance via MC-CDMA's ability to support both CDMA and frequency diversity benefits, respectively.

This letter provides a novel method for doubling throughput in time division multiple access (TDMA) systems. Specifically, with pseudo-orthogonal positioning of carrier interferometry pulse shapes, a TDMA system is designed to support twice as many real symbols in a slot, without increasing bandwidth or slot duration. With regard to performance, the doubling of throughput comes at the cost of only 1-2 dB performance degradations at probability of error of 10/sup -2/.

Applying carefully-selected time-varying phases (delays) to array elements of an adaptive antenna, the beam pattern oscillates in a controlled manner. This creates a time varying channel with a controllable coherence time. With an adaptive antenna at the base station (BS) and a single omnidirectional antenna at the mobile, the controllable coherence time is used by the mobile to exploit time diversity and enhance performance. In this work, assuming an oscillating-beam-pattern antenna array at the BS, the channel is properly modeled and the coherence time is evaluated. A so-called geometric-based stochastic channel model is presented, assuming a circular coverage area, and the channel is simulated in an urban environment. We demonstrate the relationship between coherence time and the antenna array control parameters and show that seven-fold-diversity can be created via small beam pattern oscillation.

This paper introduces a novel merger of OFDM systems, MIMO systems, and carrier interferometry (CI) spreading codes. Specifically, previous works have illustrated the performance benefits of (1) applying CI spreading codes to OFDM and (2) merging MIMO and OFDM systems. In this paper, OFDM systems are combined with both a MIMO system and CI spreading codes, resulting in the so-called MIMO-CI/OFDM system, capable of very reliable communication at SNRs previously possible only with channel coding.

Tapped delay line RAKE receivers are commonly used to achieve path diversity gain in DS-CDMA systems: Here, a bank of correlators is used to separate the multipath components and a combiner coherently recombines the multipath energies. In this paper, the optimal combining techniques for DS-CDMA RAKE receivers (under different criteria) are introduced. Specifically, based on the maximum likelihood criteria, optimal combining techniques are derived and discussed for the following scenarios: (1) channel-fade-information is not available at the receiver; (2) a statistical characterization of the channel fades is available at the receiver, but the actual, instantaneous fade information is not; and (3) the instantaneous channel fade information is available at the receiver. This paper shows that maximum ratio combining (MRC), typically considered the optimal combining scheme when fade parameters are perfectly tracked, is sub-optimal. We present the optimal alternative to traditional MRC.

In this work, we propose an innovative high performance, high throughput direct sequence spreading (DSS) ultra wideband (UWB) system. Our proposed system employs a novel multi-carrier pulse waveform at the UWB transmit side: At the receiver side, the received DSS UWB pulse is decomposed into its subcarriers and recombined to (1) exploit diversity in the frequency domain and (2) provide resistance to inter symbol interference (ISI) and/or multi-access interference (MAI). As a direct result, the proposed frequency-based UWB DSS system is shown to significantly outperform time-based DSS UWB systems, offering significant gain in throughput (up to 32 fold) without performance degradation, or, alternatively, avoiding error floors due to MAI that limit the performance of time-based systems.

In the author's earlier work, we demonstrated how performance degradation and PAPR concerns in OFDM can be overcome by application of carrier interferometry (CI) spreading codes. In this work, the authors employ RF test equipment and analyze the practical performance of OFDM (orthogonal frequency division multiplexing) based IEEE 802.11a WLAN vs. their proposed carrier interferometry (CI) OFDM based WLAN. Specifically, RF test results (in a typical indoor office environment) are used to analyze the proposed CI/OFDM and CI/COFDM technologies. It is shown that in a typical office environment, at a bit error rate of 10/sup -3/, the CI technology gains 5-7 dB over current OFDM.

In this work, the authors introduce the concept of spectral sharing in multi-system environments by application of MC-CDMA technology. The proposed MC-CDMA system supports spectral sharing via dynamic carrier allocation: the orthogonal carriers that make up a transmit signal are borrowed/shared between multiple systems. The resulting system not only supports increased spectral efficiency, but simulations indicate improved BER performance as well. It is hoped that this exploration will serve as a useful beginning in the emergence of a highly efficient spectral exchange.

The paper introduces to orthogonal frequency-division multiplexing (OFDM) systems a novel pseudo-orthogonal carrier interferometry spreading code which spreads each parallel data stream over all the OFDM carriers. Pseudo-orthogonal carrier interferometry (PO-CI) spreading codes are carefully selected to introduce the following benefits to OFDM: up to 2N parallel data streams can be coded onto N carriers, with little degradation in performance; when rate 1/2 channel coding is applied in addition to PO-CI spreading codes, the resulting binary phase-shift keying OFDM systems demonstrate the performance of coded OFDM and the throughput of uncoded OFDM; PO-CI codes are carefully selected to spread in a manner which eliminates the peak-to-average power ratio problems characteristic of traditional OFDM.

This paper introduces a novel chip shaping scheme increasing the network capacity in DS-CDMA systems without any increase in. bandwidth or chip rate, and without performance degradation. The chip shape corresponds to an interferometry pattern created by the superposition of N carriers. Two sets of orthogonal chip shapes with minimum inter-chip interference are positioned pseudo-orthogonally (in time) within a single symbol duration, allowing the novel system to support many more chips in the same symbol duration and bandwidth. Simulations performed over Rayleigh fading channels indicate the new chip shaping (and corresponding detection strategy) enables 100% gains in DS-CDMA network capacity without any loss in performance. With the exception of chip shape and receiver design, this new system retains all the features of a conventional DS-CDMA system.

In traditional BFSK, two distinct carrier frequencies are used to represent binary '1' and binary '0'. In this paper, we propose transmitting multiple, orthogonal, in-phase sub-carriers around two carrier frequencies to represent the binary information. We demonstrate that this technique is spectrally efficient when compared to traditional BFSK. Performance and data rate benefits are also demonstrated in both non-coherent and novel coherent reception techniques. Moreover, while traditional BFSK is not employed in channels that are frequency selective, we show that with coherent reception, the new FSK scheme can be used in frequency selective channels to exploit frequency diversity benefits.

WLANs (wireless local area networks) have emerged as a powerful architecture capable of supporting the requirements of broadband wireless communications. The IEEE 802.11a 5 GHz WLAN standard employs OFDM in its physical layer. This paper introduces carrier interferometry OFDM to the current 802.11a WLAN, and demonstrates that the corresponding small changes to the traditional OFDM scheme lead to notable improvements in probability of error performances and a doubling in throughput. Calling the modified WLAN system pseudo-orthogonal carrier-interferometry WLAN (or PO-CI-WLAN for short), we show that in office buildings, at a bit error rate of 10/sup -3/, PO-CI-WLAN offers a 3 dB performance gain over the IEEE 802.11a 5 GHz WLAN and simultaneously doubles the throughput.

We merge a smart antenna array with CI/DS-CDMA, a novel implementation of DS-CDMA where chips have a shape referred to as the CI (carrier interferometry) chip shape and are decomposable into N narrowband frequency components. In the antenna array, by applying suitable time-varying phases to the elements, we create small movement (oscillation) in the antenna array's pattern, while steering the main lobe to the position of the intended user. The oscillating antenna pattern creates a time-varying channel with a controllable coherence time. This, in turn, provides transmit diversity in the form of a time diversity gain at the mobile receiver side. Thus, at the receiver, three stages of combining are available: 1) combining time components of the received signal within symbol duration T/sub S/ (each experiencing a different fade) to enhance performance via time diversity; 2) combining frequency components which make up the CI/DS-CDMA chip to enhance the performance via frequency diversity; 3) combining across chips to eliminate interfering users. Employing CI/DS-CDMA with the proposed smart antenna at the base station, we achieve: 1) very high capacity via the merger of SDMA (directionality of antenna array) and CDMA; 2) very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. We focus on the performance benefits of the proposed system.

This paper proposes a novel scheme which doubles capacity in MC-CDMA systems without any cost in bandwidth and with negligible cost in performance. Specifically: (1) complex spreading codes are used instead of conventional real value spreading codes; and (2) two groups of orthogonal complex spreading codes are used simultaneously, where minimum cross-correlation exists between the two groups. Simulations performed over Rayleigh fading channels using these novel codes demonstrate that the proposed scheme enables gain of 100% in terms of MC-CDMA capacity with negligible performance losses.

OFDM (orthogonal frequency division multiplexing) is susceptible to poor probability of error performance in fading channels. To enhance OFDM's performance, many architectures utilize channel coding. The addition of coding, adds both redundancy and frequency diversity, but comes at a cost of reduced overall throughput (typically by a factor of 2). This paper introduces a novel carrier interferometry phase coding to enhance the performance in OFDM systems without bandwidth expansion or decreased throughput. It is shown that at a bit error rate of 10/sup 3/, this method gains 14 dB over OFDM, equaling the performance of COFDM. A system is now available demonstrating the benefits of coded OFDM, which maintains the throughput of OFDM. The cost is one of increased receiver complexity.

Applying proper time-varying phases (delays) to the array elements of an adaptive antenna, its beam pattern is carefully controlled to generate an oscillating beam pattern. This creates a time varying channel with a controllable coherence time. With an adaptive antenna at the base station (BS), the controllable coherence time is used by the mobile station (MS) to exploit time diversity and enhance performance. In this work, using an oscillating beam pattern antenna array in the BS, the channel is properly modeled to evaluate the coherence time in the MS. A so-called geometric-based stochastic channel modeling (GSCM) scheme is presented, which allows us to model this new time-varying channel and to investigate the coherence time. We demonstrate the relationship between coherence time and the antenna array control parameters.

This paper proposes a novel maximum likelihood combining (MLC) scheme for MC-CDMA systems. Currently, minimized mean square error combining (MMSEC) is widely considered the best combining scheme for MC-CDMA. The MLC proposed in this paper is optimal from the standpoint of minimizing the probability of error performance. It is shown that MLC is very close to MMSEC in a fully loaded system, justifying the selection of MMSEC over other combining schemes. Moreover, when the load is small (as measured by number of users), MLC is shown to outperform MMSEC (and, other combining schemes).

We introduce a novel merger of multi-input single-output (MISO) systems and MC-CDMA (multi-carrier code division multiple access) systems. Here, each group of Q carriers in the N-carrier MC-CDMA system (Q

By applying carefully selected time-varying delays to the array elements of a smart antenna located at the base station (BS), small oscillations are generated in the beam pattern. These oscillations create a time-varying channel demonstrating intra-symbol time variation and characterized by coherence time T/sub C/. At a single-antenna mobile station (MS), the time-varying channel (with coherence time T/sub C/) creates a time diversity which is exploited to enhance the mobile's performance (by introducing oversampling to the mobile receiver). We present a channel model which characterizes the time-varying channel that results from beam pattern oscillation. We then use our channel model to evaluate the coherence time, T/sub C/, at the mobile station (MS). The channel model presented corresponds to the so-called geometric-based stochastic channel model (GSCM), with a semi-elliptic coverage area. This geometric approach allows us to stochastically model the parameters of the time-varying channel impulse response. Simulations based on the GSCM show that 7-fold time diversity can be exploited at the MS (when beam pattern movement is small), which significantly improves the MS receiver probability-of-error performance.

Abstract Multi‐carrier technologies in general, and OFDM and MC‐CDMA in particular, are quickly becoming an integral part of the wireless landscape. In this first of a two‐part survey, the authors present the innovative transmit/receive multi‐carrier implementation of TDMA and DS‐CDMA systems. Specifically, at the transmit side, the pulse shape (in TDMA) and the chip shape (in DS‐CDMA) corresponds to a linear combining of in‐phase harmonics (called a CI signal). At the receiver side, traditional time‐domain processing (equalization in TDMA and RAKE reception in DS‐CDMA) is replaced by innovative frequency based processing. Here, receivers decompose pulse (or chip) shapes into carrier subcomponents and recombine these in a manner achieving both high frequency diversity gain and low MAI. The resulting system outperforms traditional TDMA and DS‐CDMA systems by 10–14 dB at typical BERs, and, by application of pseudo‐orthogonal pulse shapes (chip shapes), is able to double system throughput while maintaining performance gains of up to 8 dB. Copyright © 2002 John Wiley & Sons, Ltd.

Abstract Multi‐carrier technologies in general, and OFDM and MC‐CDMA in particular, are an integral part of the wireless landscape. In this second part of a two‐part survey, the authors present an innovative set of spreading codes known as CI codes, and demonstrate how these significantly increase performance and capacity in OFDM and MC‐CDMA systems, all the while eliminating PAPR concerns. Regarding OFDM: the spreading of each symbol over all N carriers using CI spreading codes (replacing the current one symbol per carrier strategy) are presented. CI codes are ideally suited for spreading OFDM since, when compared to traditional OFDM, CI‐based OFDM systems achieve the performance of coded OFDM (COFDM) while maintaining the throughput of uncoded OFDM, and, at the same time, eliminate PAPR concerns. When applied to MC‐CDMA, CI codes provide a simple means of supporting 2N users on N carriers while maintaining the performance of an N‐user Hadamard Walsh code MC‐CDMA system, i.e., CI codes double MC‐CDMA network capacity without loss in performance. The CI codes used in OFDM and MC‐CDMA systems are directly related to the CI pulse (chip) shapes used to enhance TDMA and DS‐CDMA (see part 1): hence, the CI approach provides a common hardware platform for today's multi‐carrier/multiple‐access technologies, enabling software radio applications. Copyright © 2002 John Wiley & Sons, Ltd.

In this paper, a smart antenna array is located at the base station (BS). Time-varying delays are applied to the array elements. These time-varying delays create a small oscillation in the beam pattern, which in turn leads to a time-varying channel. At the single-antenna mobile station (MS), the time-varying nature of the channel is exploited to achieve time diversity benefits. In this work, we present a channel model for the time-varying channel, and use our proposed model to evaluate the coherence time at the MS. A so-called geometric-based stochastic channel model (GSCM), with a semi-elliptic coverage area, is presented. This geometric approach allows us to stochastically model the parameters of the time-varying channel impulse response. Simulations based on the GSCM allow for the characterization of coherence time and its relationship to smart antenna control parameters.

OFDM (orthogonal frequency division multiplexing) is susceptible to high peak-to-average power due to an unstable envelope. Many solutions have been utilized in order to decrease the high peaks that are possible, but in these cases complexity is also added to the system architecture. In our earlier work, we introduced CI codes as a powerful tool to increase OFDM performance. This paper shows how carrier interferometry phase coding eliminates peaks in the signal envelope and in effect the problems associated with large PAPR.

One important requirement for next generation wireless communication systems is the ability to support a wide range of high rate data services. Despite advances in efficient modulation and multiple access technologies, very high data rate transfer will still require ultra-wide frequency bands. Traditional DS-CDMA systems operate over one single continuous bandwidth, and with the limited spectrum available from the FCC auctioned off in small blocks, it will not be possible for DS-CDMA to operate over a contiguous ultra-wide frequency band. This paper demonstrates how a novel chip shaping scheme, designed specifically for DS-CDMA systems, enables DS-CDMA to operate over non-adjacent frequency bands in a way that is identical to its operation if all these bands are made contiguous. The chip shape corresponds to an interferometry pattern created by the superposition of N carriers (adjacent or non-adjacent in the frequency domain). Besides the ability to operate over non-adjacent bands, this novel chip shaping enables DS-CDMA to achieve very high performance by exploiting frequency diversity (instead of path diversity) over the combined bands. With the exception of chip shape and receiver design for operation over non-contiguous bands, this new system retains all the features of a traditional DS-CDMA system.

Whenever the channel coherence time is less than the symbol duration, a mobile station (MS) receiver can exploit time diversity to enhance its probability of error performance. One way to ensure a channel coherence time less than the symbol duration is by use of a carefully controlled oscillating-beam antenna array at the base station (BS). Here, beam pattern movement creates small coherence times. In this paper, with an oscillating-beam-pattern antenna array at the BS, the time varying channel is modeled to evaluate the channel coherence time and the available diversity in the MS. Here, a geometric-based stochastic channel model (GSCM) is used, and a circular coverage area is assumed. For a mid-sized city center, coherence times are shown to correspond to 1/7/sup th/ the symbol duration, suggesting a 7-fold time diversity is available at the MS when the BS's antenna array pattern is carefully controlled.

Airport surface operations (aircraft servicing and maintenance, gate scheduling, and taxi operations) significantly affect the efficiency of airline flight schedules. Therefore, an optimized wireless communication system that supports surface operations can promote airline efficiency. This work presents multipath propagation measurements at airport ramp areas at 5.8 GHz. Statistical characterizations of the wireless channel, from these measurements, indicate large delay spreads (on average 14.78 /spl mu/s) and small coherence bandwidths (0.5 coherence bandwidth on the order of 12.25 Hz). These findings suggest that the radio environment at an airport offers large diversity gains that can be exploited in future spread-spectrum systems.

This work introduces an iterative design algorithm for establishing the discrete nuisance parameter space (e.g., discrete phase offset space) for application in data detection. Data detection is shown to be surprisingly robust to course nuisance parameter quantizations. A parallel receiver structure based on the discretization is introduced and its significant performance gains are summarized.

Two methods for applying simulated annealing to the trellis quantization codebook design problem are proposed. The results presented for both a Gauss-Markov source and speech samples indicate that the resulting design with simulated annealing is independent of the initial codebook. Moreover, the results are consistent with the generalized Lloyd algorithm with an initial codebook generated using the extension method. This suggests that the extension method is an effective initial codebook selection method.>

Maximum a posteriori (MAP) detection is applied to trellis quantizers operating over additive white Gaussian noise (AWGN) channels. The use of the MAP method instead of maximum likelihood is motivated by the fact that the source coder output probabilities, conditioned on the previous outputs (i.e. the state), are not equal. Simulation results indicate that by using MAP detection instead of maximum likelihood, gains as high as 0.57 dB and 2.2 dB can be achieved in terms of signal-to-quantization noise ratio (SQNR) for Gauss-Markov source and speech samples, respectively.>

The authors propose two methods of applying simulated annealing to the trellis quantization codebook design problem. The results presented for both a Gauss-Markov source and speech samples indicate that the resulting design with simulated annealing is independent of the initial codebook. Moreover, the results are consistent with the generalized Lloyd algorithm with an initial codebook generated using the extension method. This suggests that the extension method is an effective initial codebook selection method.>