Showing papers on "Spectral efficiency published in 1985"

Data communication method and apparatus

Abstract: A data stream is impressed on a carrier by forming from the data stream a succession of binary symbol words which control the modulation level of the carrier during respective modulation time intervals. To generate the symbol words from the data stream, the latter is first divided into a base bit stream (14) and one or more second bit streams (15). These second streams (15) are then subjected to error control coding before being used to define the least significant bits of the symbol words; the most significant bits are provided by the base bit stream. As a result, although the least significant bits of the transmitted symbol words (IV,III,II,I) are more prone to noise corruption than the most significant bits this tendency is compensated for by the error coding employed. The overall effect is to minimize power requirements while retaining good bandwidth efficiency.

Spectrum efficiency of GMSK land mobile radio

Abstract: Gaussian-filtered minimum-shift keying (GMSK) is a constant envelope and narrow-band modulation suitable for power- and band-limited digital radio communication. From the viewpoint of efficient spectrum use by land mobile radio, geographical reuse of cochannels as well as power spectrum compactness are desired. The output power spectrum of GMSK modulation can be made compact, at a sacrifice of co-channel interference protection. Parameters for optimizing GMSK are determined maintaining a compromise between co-channel reuse and power spectrum compactness.

Cellular spectrum efficiency via reuse planning

Abstract: The design of cellular systems impacts spectrum efficiency and service quality via several design choices and techniques. The reuse pattern "N" and sector plan are choices that trade off spectrum efficiency and voice quality. Overlaid cells, channel borrowing and reuse partitioning are techniques to improve that tradeoff. These effects can be quantified in generak by fairly simple rules. However, specific system growth planning depends critically on the traffic distribution in a particular city and becomes very complex in large systems. We have developed computer aids to automate growth planning and this paper reports a set of empirical studies using these aids. One of the most surprising results is how sensitive capacity is to traffic distribution.

A Condition for Stable Minimum-Bandwidth Line Codes

Abstract: By generalizing a concept on a power spectral zero at the Nyquist frequency, a condition for the line codes' capability to signal with the minimum bandwidth is established. From the condition, lower bounds of eyewidth are obtained for various values of a new system parameter called intersymbol interference sum variation (ISV). As an application of the condition, the nonminimum-bandwidth bipolar code is modified to a minimum-bandwidth code, which can be directly used in conventional bipolar signaling systems with increased bandwidth efficiency.

The Effect of Channel Coding on the Efficiency of Cellular Mobile Radio Systems

Abstract: Error correcting codes have two opposite effects on the efficiency of cellular mobile-radio systems. Although they increase the bandwidth per channel, the codes also make signals more robust and thereby reduce the required distance between users of the same frequency band. This paper reports a mathematical study of the interactions of these two effects in determining the efficiencies of a large number of sourcecode and channel-code combinations. Within a statistical performance objective (baseband SNR \geq 11 dB for 90 percent of the users), the most efficient scheme in this study has an embedded differential pulse code modulation (DPCM) source code and a rate 1/2 channel code that protects 2 bits of each 4 bit DPCM code word. Based on a conservative model of cellular transmission, we estimate that the bandwidth efficiency is 3 users/cell/MHz of system bandwidth. By contrast, there are only 1.2 users/cell/MHz with uncoded transmission and 4.5 users/cell/MHz with a rather complicated variable-rate scheme. We also observe that the embedded source code, originally devised for variable-rate operation, has a higher baseband SNR than conventional DPCM in certain fixed-rate environments.

Angle Diversity Reception for LOS Digital Microwave Radio

Abstract: Digital transmission over line-of-sight (LOS) microwave links is impaired at times by multipath fading in the propagation channel. The multipath can be a result of surface reflections, or induced by atmospheric anomalies such as strong ducting gradients. One principal method of overcoming the effects of multipath is to use a form of diversity transmission and reception. The common forms of diversity in LOS links are frequency and space, or combinations of both in severe cases. This paper describes an alternative form of diversity using angle (of arrival) diversity at the receiving terminal. This form of diversity has the advantages of a) limiting the antenna elevations required for space diversity, and b) spectral efficiency when compared with frequency diversity.

Data communication method and appartus

Abstract: A data stream is impressed on a carrier by forming from the data stream a succession of binary symbol words which control the modulation level of the carrier during respective modulation time intervals. To generate the symbol words from the data stream, the latter is first divided into a base bit stream (14) and one or more second bit streams (15). These second streams (15) are then subjected to error control coding before being used to define the least significant bits of the symbol words; the most significant bits are provided by the base bit stream. As a result, although the least significant bits of the transmitted symbol words (IV, III, II, I) are more prone to noise corruption than the most significant bits this tendency is compensated for by the error coding employed. The overall effect is to minimise power requirements while retaining good bandwidth efficiency.

New DC-free line code of minimum bandwidth with increased eye width

Abstract: A new variant of the bipolar code for improving its bandwidth efficiency is introduced. The resulting code, which can be seen as a dual code to the recently introduced VBPm, is DC-free and requires only the Nyquist bandwidth for transmission. Both its duality with VBPm and its improvement in eye width even over that of modified duobinary are presented.

Modem Design using Continuous Phase Modulation with Coding

Abstract: The combination of coding and low index modulation can result in both bandwidth and power efficient modem design. The low index modulation format is obtained by using a frequency division and multiplication network to alter the modulation index of ? for convertioned MSK to a lower value. This lower value modulation index in concert with restricted range encoding provides a system that can achieve a 2 bits/sec/Hz bandwidth efficiency at a power level equivalent to that required for MSK. The design concepts are such that data rates in the hundreds of megabits/second are practical.

An optimized bandwidth efficient demand assigned protocol for integrated Mobile Satellite Services

Abstract: This paper describes the design of a demand assigned protocol based on bandwidth efficiency for integrated services of a Mobile Satellite System (MSS). An MSS provides data (closed-ended) and voice (open-ended) communications services for a large number of mobile users dispersed over a wide geographical area. Each mobile requests its desired service through a designated set of channels to a network management center. Either pure or slotted ALOHA random access scheme can be used to make connection requests, while data and voice communications are demand assigned. All channels have equal bandwidth and can be adaptively used for reservation requests, data connections or voice connections to maximize the bandwidth utilization. In this paper, perfect communications channels are assumed. It has been shown that, for the case considered, using the slotted ALOHA scheme for making connection requests can save about 30 percent on the total number of channels over using the pure ALHOA scheme.