David A. Wiegandt

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry spreading codes

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.

Overcoming peak-to-average power ratio issues in OFDM via carrier-interferometry codes

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.

High-performance carrier interferometry OFDM WLANs: RF testing

In the authors 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.

The elimination of peak-to-average power ratio concerns in OFDM via carrier interferometry spreading codes: a multiple constellation analysis

Orthogonal frequency division multiplexing (OFDM) demonstrates symbol-by-symbol fluctuations in peak-to-average power ratio (PAPR), a direct consequence of independently modulated carriers. This, in turn, leads to inefficient operation of the transmit power amplifier, and/or in-band and out-of-band distortion due to power amplifier saturation. This paper extends our previous work, which explains how carrier interferometry (CI) spreading codes may be applied to OFDM (creating CI/OFDM) to eliminate PAPR fluctuations. Specifically, we analyze the PAPR benefits of CI codes in higher-order constellation OFDM systems (QPSK, 16-QAM, and 64-QAM OFDM). This work confirms that the proposed technique (of spreading the data symbols onto all carriers) ensures the elimination of high peaks in the signal envelope (thereby eliminating the PAPR problem): It is further shown that the choice of constellation size does little to change the PAPR benefits of the CI spreading technique.

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry coding

OFDM (orthogonal frequency division multiplexing) is susceptible to poor probability of error performance in fading channels. To enhance OFDMs 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.

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry type 2

OFDM (orthogonal frequency division multiplexing) demonstrates poor probability of error performance in fading channels, and hence many OFDM systems utilize channel coding. The addition of this coding, adding both redundancy and frequency diversity, comes at a cost of reduced overall throughput (typically by a factor of 2). PO-CI/OFDM is as a new methodology to enhance performance in OFDM systems, via channel coding, without bandwidth expansion or decreased throughput. Specifically, by placing 2N symbols pseudo-orthogonally on the N OFDM carriers (via the use of spreading codes) and by introducing rate 1/2 convolutional coding, PO-CI/OFDM achieves the benefit of channel coding in OFDM without the cost of throughput reduction. It is shown that, in BPSK systems, at a bit error rate of 10/sup -3/, this method gains 15 dB over OFDM, equaling the performance of traditional coded OFDM (COFDM) without the throughput reduction.

High-performance 64-QAM OFDM via carrier interferometry spreading codes

OFDM (orthogonal frequency division multiplexing) is an excellent technology that will almost certainly play a large role in next generation wireless communication systems. However, in OFDM, no frequency diversity is exploited to improve BER performance. Todays OFDM systems attempt to overcome this limitation by application of channel coding and interleaving, which requires a reduction in throughput. In our earlier work, we showed how carrier interferometry (CI) codes may be used to spread OFDM symbols over all N subcarriers to exploit frequency diversity without loss in throughput. However, only BPSK was considered in the earlier work. In this paper, we extend the proposed CI/OFDM (carrier interferometry with OFDM) system by updating it for application with QAM modulation schemes. (For example, minimized mean square error combining (MMSEC) is derived for CI/OFDM with QAM modulation schemes.) Simulation results over multi-path fading channels show that 64QAM CI/OFDM significantly outperforms 64QAM OFDM at the cost of a small increase in complexity.

The road to 4G: two paradigm shifts, one enabling technology

A new wireless vision is unfolding, one in which the cellular-based handheld emerges as an increasingly integral part of our everyday lives. As we bring our wireless visions to light, it is becoming evident that the desire for information may quickly surpass the limited bandwidth capabilities of the standardized 3G network. The growing discontent with the throughput limitations of 3G is leading to the rapid development of 4G, intended to be the Nirvana of wireless communications. This work contends that two fundamental paradigm shifts must emerge if 4G is to succeed. First, the work presents a new bandwidth sharing/allocation strategy, blending the best of traditional spectral allocation strategies with the emerging concept of ultrawideband wireless. The second shift presented in the paper refers to the transformation of handhelds, presenting our vision of the transition from hardware defined to software defined radio. To enable these two paradigm shifts, the work presents an underlying multi-carrier technology capable of supporting both transformations

Higher-speed, higher-performance 802.11a wireless LAN via carrier-interferometry orthogonal frequency division multiplexing

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.

High-performance, high-throughput IEEE 802.11 DSSS WLAN via carrier-interferometry chip-shaping

WLAN (wireless local area networks) promise to combine the mobile connectivity of the wireless world with the speed and robustness of current wired systems. With IEEE 802.11, WLAN are emerging that support a variety of data types as well as rates. This paper introduces a novel carrier-interferometry chip-shaping filter to the DSSS implementation of IEEE 802.11 WLAN. This technique is capable of improving performance and doubling the throughput of the current DSSS system. It is shown that, at a bit error rate of 10/sup -3/, the proposed method gains 4 dB over the current DSSS WLAN while offering twice the throughput.