Handover is the mechanism that transfers an ongoing call from one cell to another as a user moves through the coverage area of a cellular system. As smaller cells are deployed to meet the demands for increased capacity, the number of cell boundary crossings increases. The author presents an overview of published work on handover performance and control and discusses current trends in handover research. He discusses investigations that are applicable to a single tier of cells. He focuses on macrocells, but includes a brief discussion on how things change as cell sizes shrink. By assuming an overlay of macrocells and microcells he summarizes issues and approaches unique to such systems.

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Trends in handover design

Multimode, multi-function, multiple modulator-demodulator (modem) system containing a fingerprint sensor, detection, identification, authentication, and processing device for one or multiple fingerprint information to activate one or multiple modulators for signal transmission and generation of authentication information signals. A location information receiver and a processor device for processing and combining the location information and fingerprint information activated signals with one or more additional user generated signals. Processed, combined signals are provided for filtering and/or spread spectrum encoding and/or cross-correlating and connection to one or more modulators and transmitters.

Multimode communication system

A radio frequency identification (RFID) device, locator, wired and/or wireless communicator system comprising one or more than one antennas for receiving Radio Frequency (RF) signals from one or more RFID and or location determining and/or communication transmitters. The system has one or more receivers and demodulators for reception and demodulation of signals to baseband signals. A processor circuit processes the baseband signals and provides them to a cross-correlator circuit for cross-correlating the processed baseband signals and for generation of cross-correlated baseband signals. One or more modulators modulate the baseband signals and provide them to one or more transmitters. circuitry.

Location finder, tracker, communication and remote control system

An antenna array-based base station receiver structure for wireless direct-sequence code-division multiple-access (DS/CDMA) with M-ary orthogonal modulation is proposed. The base station uses an antenna array beamformer-RAKE structure with noncoherent equal gain combining. The receiver consists of a "front end" beamsteering processor feeding a conventional noncoherent RAKE combiner. The performance of the proposed receiver with closed loop power control in multipath fading channels is evaluated. Expressions for the system uncoded bit-error probability (BEP) as a function of the number of users, number of antennas, and the angle spread are derived for different power control scenarios. The system capacity in terms of number of users that can be supported for a given uncoded BEP is also evaluated. Analysis results show a performance improvement in terms of the system capacity due to the use of antenna arrays and the associated signal processing at the base station. In particular, analysis results show an increase in system capacity that is proportional to the number of antennas. They also show an additional performance improvement due to space diversity gain provided by the array for nonzero angle spreads.

Performance of wireless CDMA with M-ary orthogonal modulation and cell site antenna arrays

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. >

Effects of diversity power control, and bandwidth an the capacity of microcellular CDMA systems

The author proposes that one can overlay an existing GSM cellular network with a broadband CDMA cellular system utilizing direct-sequence spread spectrum alone with agile notch filters at the base station. Notch filter depths of 35 dB on receive and 20 dB in transmit were found to be adequate. Capacity calculations show that the B-CDMA overlay can approximately quadruple the nominal capacity of GSM, which is 16 channels per sector, by providing an additional 51 voice channels at 16 kbps each. Also, the author has calculated that the B-CDMA mobile transmits on average with 16 dB less power than the GSM mobile, while the CDMA base transmit power per channel would be about 5.5 dB less than the GSM base due to the lower CIR required by the B-CDMA overlay system. >

The capacity of broadband CDMA overlaying a GSM cellular system

Bandwidth is the most important parameter of a code division multiple access (CDMA) system. It is governed by the system chip rate and affects capacity, fade margin, data rate, voice quality, performance in indoor and outdoor environments, transition plan, frequency management, overlay capability, and adaptive power control. The author discusses how each of these parameters is affected by the choice of bandwidth. A comparison is made between the capacity of a B-CDMA system in the cellular and PCS bands.

Broadband spread spectrum multiple access for personal and cellular communications

The authors address the mutual interference caused by the coexistence of narrowband code division multiple access (N-CDMA) and narrowband cellular telephone technologies, i.e., advanced mobile phone system and time division multiple access (AMPS and TDMA). It is shown that when adjacent service areas are using AMPS or TDMA, a dead zone of up to two cells is required before N-CDMA can be deployed. The resulting capacity of the N-CDMA service area is lessened to an extent dependent upon the service area geometry. The dead zone can be extensive enough where the N-CDMA would yield only marginal capacity improvement over AMPS and TDMA.

Impact on capacity to AMPS jamming CDMA/CDMA jamming AMPS in adjacent cells

A direct sequence spread spectrum code division multiple access (CDMA) communication system for cellular or PCN applications should be designed to use the entire bandwidth allocated. In this way the peak power spectral density is minimized. However, some CDMA systems have been designed to have a bandwidth which is much less than the allocated bandwidth. Such narrowband CDMA (N-CDMA) systems lack the LPI characteristics of spread spectrum. The authors address the mutual interference caused by the coexistence of N-CDMA and existing narrowband cellular telephone technologies (AMPS FDMA or TDMA). It is shown that when adjacent service areas are using AMPS or TDMA a dead zone of up to two cells is required before N-CDMA can be deployed. The resulting capacity of the N-CDMA service area is lessened to an extent dependent upon the service area geometry. The dead zone can be extensive enough where the N-CDMA would yield only marginal capacity improvement over AMPS and TDMA. Furthermore, significantly higher N-CDMA mobile transmit power would be required than would be true without adjacent cell interference. >

D.L. Schilling

Papers

The capacity of broadband CDMA overlaying a GSM cellular system

Broadband spread spectrum multiple access for personal and cellular communications

Impact on capacity to AMPS jamming CDMA/CDMA jamming AMPS in adjacent cells

Capacity limitations due to adjacent cell dissimilar technologies

Broadband Spread Spectrum Multiple Access For Personal And Cellular Communications