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Wireless Personal Communications: What Is It?
Donald C. Cox
Wireless PCS is in a chaotic and transitionary state; it will evolve
into two main classes - "high-tier" systems that focus on highly
mobile voice communications, and "low-tier" systems that
minimize cost, maximize the number of users per cell, and provide
voice and data capability.
- Classes of PCS: Messaging (voice mail, fax, e-mail),
paging (broadcast with no return channel), real-time two-way
communications, and "agents& represent broad classes of PCS.
These classes should work across different geographical scales, with
- Digital cordless: CT-2, DECT - 32kb/s ADPCM, 10-50ms RTT,
4QAM modulation, time-division duplex are the common features of these
- High-tier PCS: high-tier PCS is the catch-phrase for
early digital cellular systems such as IS-54, IS-95, GSM, and DCS-1800.
Such systems are characterized by complex modulation and speech coding
techniques and large macro-cells on the order of 0.5-3.0 kilometers, with
the goal of maximizing both users/MHz and users per cell, implying high
power consumption, network complexity, and end-end latency.
- Wide-area data: ARDIS, CDPD, RAM, and now Metricom are
examples of commercialized technologies. Typically such services
exhibit high mobility, low data throughput, and high latencies. In
the face of low-tier PCS, the future of such services is uncertain.
- WLAN: Very desirable properties, but currently unprofitable
in spite of severe commercial competition. Two main designs include
centralized coordination and ad-hoc self-organizing LANs.
- Low-Tier PCS: Evolutionary trends are towards microcell
coverage for frequency reuse and low-power benefits, overlay networks
of LAN, MAN, and WAN wireless systems, low-complexity coding and
efficienct modulation, and FDMA or CDMA to relax time synchronization
This paper gives describes the current state of wireless communications
and speculates on the future, from a telecommunications perspective.
The evolutionary trends presented are strongly argued and supported
with evidence, and the facts described are accurate without being
- Nearly all systems or other high-level issues involved with
wireless communications are totally ignored.
- The future demand for high-speed data services that exhibit high
mobility seems to be underestimated; wireless voice and paging services
are overemphasized. (This is probably because the author is a
- Much speculation is stated as fact rather than possibility.
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