摘要:
A CDMA cellular radio-telephone system (FIG. 2) comprises a packet-switched communications network (202, 207, 201) that interconnects cells (base stations; 202) with each other and with the public telephone network (100). A unique combination of a static addressing plan that uses a different LAPD DLCI (302 in FIG. 7) for each unidirectional virtual call path, direct cell (202)-to-cell and cell-to-call-processing unit (264 in FIG. 5) control information exchanges, and packet-switching techniques that permit call traffic and control communications to share call paths and permit different call paths to share physical resources, is applied to call processing. This enables soft handoffs (FIGS. 27-29) to be handled in a manner transparent to the parties to the call and without significant involvement of system control elements (134 and 261 in FIG. 2) whose involvement would adversely impact the system's call-handling capacity. It also enables soft handoffs to occur without change of the call processing unit that is handling the call, so that a single call processing unit continues to handle the call from start to finish through even multiple soft handoffs.
摘要:
A wireless-access communications system, such as a CDMA cellular radio-telephone system (FIG. 2), comprises a packet-switched communications network (202, 207, 201) that interconnects cells (base stations; 202) with each other and with the public telephone network (100). Traffic of individual calls is packetized, and packet-bearing frames (300 in FIG. 7) of a plurality of calls are then statistically multiplexed and frame-relayed through the network to yield the high capacity, efficiency, and speed of traffic transport and handoff required for a CDMA cellular system. At each call processing unit (264 in FIG. 5), individual calls are handled by individual service circuits (602 and 612) which perform speech-processing functions such as coding and decoding, tone insertion, and echo cancellation, and packet-to-circuit-switched-PCM traffic conversion. Processors (602) adapt call processing unit timing to compensate for asynchrony between cells and call processing units and variations in call path transmission delays. Cell-to-cell communications, fixed call path addressing, and packetized control message transfers ensure that the same service circuit handles a call through even multiple soft handoffs (FIGS. 27-29) and efficiently communicates simultaneously with all cells involved in the handoff without involvement of system control entities and negative effect on system call-handling capacity. Both coded (packet-switched) and uncoded (circuit-switched) radio-telephone traffic are accommodated side-by-side. Wherever possible, existing and proven technology and component units are used to achieve low cost and high reliability.
摘要:
Supervisory audio tones received from a mobile telephone unit are converted from analog to digital form. The tone is then converted to a complex number by bifurcating the tone path and multiplying one path by a sine function and the other path by a cosine function. The complex numbers are accumulated and the frequencies where significant power exists is found using the discrete Fourier transform. If the power at an assigned frequency exceeds a threshold, the corresponding supervisory audio tone is declared to have been detected.
摘要:
Received baseband data signals, in the form of signals having at least one level transition per symbol indicative of symbol information state, are sampled (17) at a rate much higher than the symbol rate. The samples are used to control the direction of counting (20) of local clock (12) signals recurring at that higher rate during symbol subintervals of predetermined duration. Counts produced during adjacent subintervals are processed (FIGS. 4 and 5) to produce several different results such as recognition of the start of an asynchronously occurring data message, acquisition and tracking of symbol phase in the message, and detection of symbol information states.