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One of the main benefits of the cyclostationary beamforming algorithms is their ability to extract signals from co-channel interference with only a knowledge of the cycle frequency. In this paper, we study the popular cyclostationary beamformers, and propose five new algorithms, namely, the adaptive cyclic adaptive beamforming (ACAB), adaptive cross-SCORE (ACS), constrained least-squares (CLS), adaptive phase-SCORE (APS), and maximal constrained autocorrelation (MCA) algorithms. All these algorithms are adaptive and have a computational complexity of O(n 2) complex multiplications, where n is the number of array elements. A comparative study of these algorithms is made based on numerical simulations. Each of these algorithms has specific application scenarios. The ACS and the APS algorithms are particularly suited for very adverse signal environments. The ACAB, MCA and cyclic adaptive beamforming (CAB, from the work of Wu and Wong) algorithms can provide good performance in the case of medium or weak interference, while the CLS algorithm is especially suitable for weak interference. The CAB algorithm is shown to be a special case of the least-square self-coherent restoral (LS-SCORE) algorithm. Some insights as to how one can assign carrier frequency and symbol rate during digital modulation are also suggested. The proposed adaptive algorithms are easy to implement, and thus are very promising for applications in wireless and mobile communications. more...

Introduction OFDM, also known as simultaneous MFSK , has been widely implemented in high-speed digital communications in delay-dispersive environments. It is a multicarrier modulation (MCM) technique. OFDM was first proposed by Chang in 1966. Chang proposed the principle of transmitting messages simultaneously over multiple carriers in a linear band-limited channel without ISI and ICI. The initial version of OFDM employed a large number of oscillators and coherent demodulators. In 1971, DFT was applied to the modulation and demodulation process by Weinstein and Ebert. In 1980, Peled and Ruiz introduced the notion of cyclic prefix to maintain frequency orthogonality over the dispersive channel. The first commercial OFDM-based wireless system is the ETSI DAB standard proposed in 1995. A wide variety of wired and wireless communication standards are based on the OFDM or MCM technology. Examples are digital broadcasting systems such as DAB, DVB-T (Terrestrial DVB), and DVB-H; home networking such as digital subscriber line (xDSL) technologies; wireless LAN standards such as HyperLAN/2 and IEEE 802.11a/g/n; wireless MANs such as IEEE 802.16a/e (WiMAX), ETSI HiperACESS, IEEE 802.20 (mobile-Fi), WiBro, and HiperMAN2; wireless WANs such as 3GPP LTE and 3GPP2 UMB; powerline communications such as HomePlug; wireless PANs such as UWB radios (IEEE 802.15.3a/3c/4a). It is commonly deemed that OFDM is a major modulation technique for beyond-3G wireless multimedia communications. Features of OFDM technology In OFDM technology, the multiple carriers are called subcarriers , and the frequency band occupied by the signal carried by a subcarrier is called a sub-band . more...

Introduction UWB technology, also known as impulse radio , was first used to transmit Morse codes by Marconi in 1900 through the transatlantic telegraph. Modern UWB technology has been used for radar and communications since the 1960s. Like CDMA systems, early UWB systems were designed for military covert radar and communications. The early applications of UWB technology were primarily related to radar, driven by the fine-ranging resolution that comes with large bandwidth. UWB technology for wireless communications was pioneered by Scholtz. With the intent of operating UWB in an unlicensed mode that overlaps licensed bands, the FCC issued rules under the FCC Rules and Regulations Part 15 for UWB operation in February 2002. The FCC defined a UWB transmitter as “an intentional radiator that, at any point in time, has a fractional bandwidth equal to or greater than 0.20, or has a UWB bandwidth equal to or greater than 500 MHz, regardless of the fractional bandwidth”. “The UWB bandwidth is the frequency band bounded by the points that are 10 dB below the highest radiated emission, as based on the complete transmission system including the antenna.” According to the FCC regulations, the transmitter sends pulses with a bandwidth of at least 500 MHz that is within the band 3.1 to 10.6 GHz, for output power densities below −41.25 dBm/MHz. The FCC Part 15 limit of 500 µV/m at 3 meters is equivalent to an effective isotropic radiated power (EIRP) of −41.25 dBm/MHz. more...

The cellular concept The cellular concept was a major breakthrough in mobile communications, and it initiated the era of modern wireless communications. It helped to solve the problem of spectral congestion and user capacity. For wireless communications, the antennas are typically required to be omnidirectional. The cellular structure divides the geographical area into many cells. A BS equipped with an omnidirectional antenna is installed at the center of each cell. Neighboring cells use different frequency bands to avoid co-channel interference (CCI). The same frequency bands can be used by different cells that are sufficiently far away. This leads to frequency reuse. For a distance D between two cells that use the same frequency bands and a radius R of the cell, the relative distance D/R between the two cells is the reuse distance . There is no CCI within a cluster of cells, where each cell uses a different frequency spectrum. The number of cells in a cluster is called the cluster size . The cluster size determines the capacity of the cellular system: a smaller cluster size leads to a large capacity. The cell shape usually takes the form of hexagon, and the overall division of space is like a beehive pattern. This is illustrated in Fig. 4.1 for cluster size 4 and reuse distance D/R ∼ 4. This hexagonal cell shape is suitable when the antennas of the BSs are placed on top of buildings with a coverage radius of a few miles, such as in the 1G mobile systems. more...