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BellcoreRed Bank, New Jersey 07701 ABSTRACTPortable radio users can access the local telecommunications network by having their radio automatically select the channel that maximizes downlink transmission quality. Corresponding uplink transmission quality will generally be different because of multipath and differences in uplink/downlink co-channel interference. A computer simulation of portable access was used to find uplink/downlink transmission quality as a function of reuse factor, propagation parameters, and traffic level. It was found that uplink transmission quality lags that of the downlink in moderate to heavy co-channel interference environments, but not unmanageably so. INTRODUCTIONIn Universal Digital Portable Communications (UDPC)[11[21 users start and maintain two-way voice and data connections through fixed radio access ports connected to the local telecommunications network. A spectrally efficient balance between transmission quality and system capacity can be achieved by reusing independently accessible time-divisionmultiplexltime-division-multiple-access (TDM/TDMA) frequency channels. A major impairment to transmission quality will therefore be co-channel interference.To establish a radio link, the portable radio selects a channel that maximizes transmission quality on the downlink. A protocol between the portable radio and the dominant port takes place on the selected channel, which if successful, results in a time-slot assignment and two-way connection. Thus, the portable radio has a major role in link control. This reduces communications and control overhead in the fixed radio network.A previous study[31 showed that downlink transmission quality can approach optimum using a readily realizable access algorithm in the portable radio. A recent paperL4' gave basic results for uplink/downlink transmission quality at access. This paper extends those results by finding two-way transmission quality for a range of frequency reuse and propagation model parameters. The effect of traffic on the TDMA uplink is given as a function of occupancy. Figure 1 shows the access scenario in the frequency reuse environment. Each port is connected to the local network through a radio network interface. THE MULTIPLE ACCESS PR\OBLEM ScenarioPorts transmit continuously in TDM format, where each time-slot contains voice or data bits, or an idle marker if not in use. Portables transmit in bursts on the uplink in their assigned time-slots. L I 3 ? I ZG l c L 7 4 1 9 1 To + i % i NETWORK Figure 1 -Portable Radio Access in the Frequency Reuse EnvironmentThe objective of access is to obtain a stable two-way radio link with good transmission quality by selecting a channel that maximizes the signal-to-co-channel-interference ratio. Cochannel interference is reduced by maximizing the distance between co-channel ports and minimizing the distance between users and their selected ports. Access AlgorithmThe portable radio access algorithm used has two stages. First, the portable tunes to each frequency channel and measures total rela...

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