Spectrum efficiency of radio data system (RDS)

The paper addresses the use of the radio data system (RDS) for datacasting road traffic information. It is concluded that, although RDS may be essential to the early phases of introduction of novel advanced traffic information systems (ATISs), FM subcarrier transmission does not offer a spectrum-efficient solution for large-scale ATIS datacasting. The conclusions are believed relevant to the spectrum-efficient design of the future datacasting networks     

Robust OFDM receivers for dispersive time-varying channels: equalization and channel acquisition

In orthogonal frequency-division multiplexing, time variations of a multipath channel lead to a loss of orthogonality between the subcarriers, and thereby limit the achievable throughput. This paper proposes a general framework for a controlled removal of intercarrier interference (ICI) and channel acquisition. The core idea behind our method is to use a finite power series expansion for the time-varying frequency response, along with the known statistical properties of mobile radio channels. Channel acquisition and ICI removal are accomplished in the frequency domain and allow for any desired tradeoff between the residual ICI level, the required training for channel acquisition, and processing complexity. The proposed approach enables a high spectral efficiency (64-quadrature amplitude modulation mode) of digital video broadcasting-terrestrial in highly mobile environments.     

Base station to vehicle communication for intelligent vehicle/highway systems (IVHS)

An optimum frequency reuse factor of 1 or 2 is proposed to minimise the average queueing delay and maximise throughput in a packet-switched microcellular network with BPSK transmission over dispersive Rician-fading channels. Thus, for intelligent vehicle/highway system data networks, frequency reuse can be substantially denser than has been suggested for circuit-switched cellular telephony networks.<>     

Performance analysis of synchronous MC-CDMA in mobile Rayleighchannel with both delay and Doppler spreads

Rapid time variations of the mobile communication channel have a dramatic effect on the performance of multicarrier modulation. This paper models the Doppler spread and computes its effect on the bit error rate (BER) for multicarrier code division multiple access (MC-CDMA) transmission and compares it to orthogonal frequency division multiplexing (OFDM). Also, we evaluate the transmission capacity per subcarrier to quantify the potential of MC-CDMA and (coded-) OFDM. We focus on linear receivers, in particular those using the minimum mean-square error (MMSE) criterion. Our channel and system models allow the computation of analytical performance results. Simulations verify some commonly used, yet critical assumptions     

Imperfect sector antenna diversity in slotted ALOHA mobile network

In a wireless network with path loss and fading channels, receiver capture is known to substantially enhance the performance of the slotted ALOHA random access protocol. The efficiency of narrowband slotted ALOHA radio networks can be enhanced further by using sector antennas, each receiving signals from a particular segment of the network area. This paper investigates the effect of realistic, i.e., partially overlapping antenna patterns and the resulting correlation of received power levels at different receiver branches. A method is derived for computing the joint throughput from two base station receivers with overlapping antennas patterns. The a posteriori information provided by the event of one message capturing one antenna is used to find conditional probabilities of capturing the other antennas as well. The paper shows that any overlap in the antenna patterns decreases the throughput, but transmissions from the overlapping area may face a larger probability of capture than signals from directions in which one antenna has maximum gain     

Code Division-Based Sensing of Illumination Contributions in Solid-State Lighting Systems

Light-emitting diodes (LEDs) have emerged as a prime candidate for the light source of the future. To enable easy user interaction with a future lighting system consisting of many LEDs, this paper proposes a method to accurately measure and estimate the local light contributions of a large set of LEDs. This is enabled through tagging the light of each LED with an unique identifier. To this end, we propose a new family of modulation and multiple access schemes in this paper, named code-time division multiple access-pulse position modulation (CTDMA-PPM) and CTDMA-pulse width modulation (CTDMA-PWM). These schemes satisfy illumination constraints, are compatible with the commonly used PWM dimming of LEDs, and meet the multi-signal separation requirements for simultaneous measurement of illumination strengths. Based on these modulation methods, the paper develops algorithms to estimate illumination. Finally, performance analyses show that even for a very large number of LEDs, the sensing performance of the proposed system satisfies the requirements up to an adequate range.     

Multi-user and self interference effects in a QPSK DS-CMA downlink with a Ricean dispersive channel

This paper derives the BER in synchronous (downlink) indoor direct-sequence code division multiple access (DS-CDMA) transmission over a Ricean multipath channel with a non-uniform delay profile. Computational results will show that the performance is much better than that predicted by models which assume that all resolvable paths have independent identically distributed (i.i.d.) power.Portions of this paper have been presented at the IEEE Asilomar Signals and Systems Conference, Nov. 1–3, 1993, Monterey, CA.     

Throughput of inhibit sense multiple access with propagation delays

A large number of terminals transmitting data packets over a common radio channel to a central base station is studied. In inhibit sense multiple access (ISMA), the base station broadcasts a busy signal when an incoming packet is being received, to inhibit other terminals from colliding transmissions. This busy signal arrives at each terminal with a propagation delay, proportional to the distance between the base station and the terminal. This leads to unfairness in the probability of successfully transmitting a data packet, since nearby terminals have more up-to-date information on the actual channel status than remote terminals. This unfairness is additional to the advantage that nearby terminals have because of the capture effect, which is also considered. The paper applies nonstationary Poisson processes to describe the random arrivals of data packets at the central receiver. It is shown that the probability of a successful attempt to transmit a packet decreases, approximately linearly with the distance between the transmitter and the central receiver. The total throughput is also assessed, and it is found that the assumption of a fixed propagation delay adopted in CSMA studies by others gives too optimistic results for ISMA. Moreover, the analysis suggests a subtle change of the fixed delay approximation that enhances its accuracy, without adding complexity. The effect of propagation delays in random access radio networks are of increasing importance, since newly developed systems are designed to transmit with increasingly high bit rates