The original intention of GSM was to support CS-based services. In particular,
they refer to voice and fax of up to 9.6 kbps. PS-based services will be better handled in the evolution
of GSM, such as GPRS [13] and EDGE [14??“16]. The benefits will take the form of increased
user capacity, efficient usage of radio resources, higher throughput rate, and so forth. Multimediabased
services and Internet access are among the many usage scenarios. Obviously, all these targeted
improvements must be able to coexist with the traditional voice network/service.
Due to the bursty nature of the PS services, a system that can dynamically allocate resources (i.e.,
time slots) depending on the user??™s demands is essential. This concept is called bandwidth on demand.
GPRS keeps the modulation scheme to GMSK, but adds additional coding methods for varying input
requirements. EDGE introduces 8-PSK modulation scheme as well as further coding methods for
varying throughput requirements. The channel baud rate and time-slot structures remain unchanged
at the physical layer.
Let us consider the EDGE system. For our sake, we will focus on the coding schemes and modulation
schemes available. There are nine coding schemes shown in Table 1.
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