3G System RF Design Considerations

The radio frequency (RF) design criteria is a set of rules or parameters that
are used by the RF Engineering department to not only design the network
and the new components that are added, such as cell sites, but also for
improving the performance of the network. The values that are included for
each of the design criteria topics is driven by the desire to offer the best service
within the monetary and technological constraints.
Therefore, the design criteria for the radio access part of a 3G system is
extremely important to establish at the onset of the design whether it is for
a new system, migrating to an new platform, or expanding an existing system.
Many aspects are associated with an RF design and surprisingly they
are common, in concept, with any radio access platform that is being utilized
by a wireless operator.
This chapter will try and consolidate many of the most important issues
concerning the generation and execution of a design criteria associated with
the radio access portion of a system. The topics that will be discussed in this
chapter are as follows:
■ RF system design procedures
■ Methodology
■ Propagation models
■ Link budget
■ Tower top amplifiers
■ Cell site design
■ RF design report
The chapter concludes with a recommended format for presenting the
design criteria in a formalized report that will list the design criteria,
assumptions, and other key issues.
In summary, the RF design process for a wireless network is an ongoing
process of refinements and adjustments based on a multitude of variables,
most of which are not under the control of the engineering department.The
RF system design process involves both RF and network engineering efforts
with implementation, operations, customer care, marketing, and, of course,
operations. However, it is important to note that although many issues are
outside the control of the technical services group of a wireless company, the
need to stipulate a design and its associated linkages is essential if there is
any desire to obtain an operating system that meets the system objective of
fulfilling the customer’s requirements.
Therefore, the RF system design process that should be followed is listed
here in summary form. The process can be used for an existing system or a
new system because the material needs to be revisited for each of the topics
when any system design takes place:
■ Marketing requirements
■ Methodology
■ Technology decision
■ Defining the types of cell sites
■ Establishing a link budget
■ Defining coverage requirements
■ Defining capacity requirements
■ Completing RF system design
■ Issuing a search area
■ Site qualification test (SQT)
■ Site acceptance/site rejection
■ Land use entitlement process
■ Integration
■ Handover to operations
It is important to note that the design process or guidelines involve not
only the establishment of the criteria, but also the realization of the design
itself.
The information needed for a system design varies from market to market
and, of course, nuances can be noticed between the different technology
platforms. However, commonality exists between markets and also technology
platforms. The following is a brief listing of the most important
pieces of information needed for a system design:
■ Time frames for the report to be based on
■ Subscriber growth projections (current and future by quarter)
■ Subscriber voice usage projection (current and forecasted by quarter)
■ Subscriber packet usage projection (current and forecasted by quarter)
■ Subscriber types (mobile, portable, packet capable, blend)
■ New features and services offered
■ Design criteria (technology-specific issues)
■ Baseline system numbers for building on the growth study
■ Cell site construction expectations (ideal and with land-use entitlement
issues factored in)
■ Fixed Network Equipmemt (FNE) ordering intervals
■ New technology deployment and time frames
■ Budget constraints
■ Due date for design
■ Maximum and minimum off loading for cell sites when new cells are
added to a design
Of course, many sources and types of information are required for an RF
design. The basic inputs usually obtained from the Marketing and Sales
organization within a wireless network are listed in this chapter. The output
from the RF design process will determine the requirements and fundamental
structure of the radio access aspects of a wireless system. A
simplified radio access structure is shown in Figure 9-1 but can apply to
any situation with the expansion of the individual components relative to
the different technology platforms utilized.
In order to design either a new system or establish the migration path
for a system, the RF design is relegated to determining the specific access
method that the subscriber will have with the wireless system. The subscriber
and base stations (Base Transceiver Stations [BTSs]) both have a
transmitter and receiver incorporated in their fundamental architecture.
Figure 9-2 is an illustration of the various components that need to be factored into the design of a system. Figure 9-2 can be used for any technology
platform and the specifics with the various network elements make up part
of the propagation analysis where Carrier to Interferer (C/I) or Energy per
bit per noise (Eb/No) values are used to determine the performance criteria
necessary for the successful transmission and reception of the information
being delivered.