A.M. Street

Indoor optical wireless systems : a review

This paper reviews the research effort to date into optical wireless communication systems, both in academic and industrial contexts. The idea of using the optical medium for wireless communications is not new, having been proposed as a means for indoor communications almost two decades ago. However, the last few years have seen an explosive interest in the potential for free space optical systems to provide portable data communications. One of the prime motivators for reconsidering the use of an optical carrier in the wireless context is the demand for greater transmission bandwidths. The radio frequency spectrum is already exceedingly congested and frequency allocations of sufficient bandwidths are extremely hard to obtain. Further, for the high bandwidth services envisaged, the use of microwave or mm-wave systems will be required, where device technology is currently either expensive or immature. Proponents of optical wireless systems argue that the optical medium is the only cost-effective way to provide high bit-rate mobile services to volume markets. This paper identifies the technical obstacles and limitations of indoor optical wireless delivery in addition to techniques for mitigating these effects and shows that infrared is a viable alternative to radio for certain applications.

High speed wireless IR-LANs using spatial addressing

Currently, there is considerable interest in infrared as an alternative medium to radio for indoor wireless communications, particularly for computer networking applications. This paper describes a novel IR-LAN link topology that employs an optical spatial-angular mapping technique which minimizes link losses and facilitates high link rates, whilst maintaining a useful coverage area. Blocking probability effects and overall system performance are examined in terms of aggregate transmission rates.

BER Performance of NRZ-OOK and Manchester Modulation in Indoor Wireless Infrared Links

This paper describes a novel approach to theevaluation of the bit error rate (BER) performance ofoptical wireless links that takes into account shotnoise, fluorescent light interference, and intersymbol interference (ISI) from both multipathdispersion and high-pass filtering (HPF) at thereceiver. The calculation of the BER is achieved withthe use of an efficient numerical technique based onnonclassical Gauss Quadrature Rules. Fluorescent lightinterference is modeled as a Fourier series expansionwith coefficients taken from measurements, whilemultipath-induced ISI is calculated by using previouslyreported IR channel models. Application of the techniquepresented here allows for the calculation of the optimumHPF cutoff frequency that minimizes the overallperformance penalty. Finally, as an application of this method, the BER performance of NRZ-OOK andManchester (2-PPM) modulation is evaluated and numericalresults are presented for different linkscenarios.

Error rate evaluation of wireless infrared links

A novel approach to the evaluation of bit error rate performance for directive optical wireless links, which takes into account shot noise, fluorescent lighting and intersymbol interference (ISI) is presented. The evaluation technique is based on nonclassical Gauss quadrature rules, with the fluorescent light and the ISI from high pass filtering being modeled mathematically. As an application of this method the BER performance of NRZ-OOK and Manchester modulation has been evaluated and numerical results are presented. It is shown that Manchester modulation is quite robust in combating fluorescent lighting interference and its performance is not critical on the selection of the HPF cutoff frequency.

Impact of planning uncertainties in designing a cellular mobile communication network

The effects of planning parameter uncertainties in designing a cellular network are presented. Potential errors are quantified and consequences in cellular planning are shown. The analytical model employed is based upon novel general expressions, derived for the exact calculation of cochannel interference probability for nonstationary terminals in combined short and long term fading conditions. In particular the required quality of information about the propagation environment, for service quality and cell capacity estimation, is analysed.

An approach to the calculation of the probability of cochannel interference for PCS/PCN cellular planning

A methodology for prediction of outage probability and probability of cochannel interference for PCN/PCS is described. The approach enables a comparison of the relative performance of different systems under varying conditions. DCS1800 and PCS1900 results illustrate the impact of implementation options on the outage probability, probability of cochannel interference, system capacity and cost.

Radio imaging for the validation of propagation predictions

This paper presents techniques for obtaining direction of arrival (DOA) information from both narrowband and wideband radio channel measurements, with the use of spatial diversity. The multipaths arriving at the receiver are presented in a photographic form, which may be directly compared with the surroundings. The use of wideband channel information allows time-gated measurements to be made of the impinging signals. This technique is ideally suited to the validation of radio cellular propagation tools.