RF Design Magazine


Indoor wireless networks: issues and answers
Apr 1, 2002 12:00 PM  By Tom Snyder, John Catlin

Implementing reliable indoor wireless voice and data networks is difficult at best. To get optimum quality of service, know what you’re up against before the system goes in.

Interference – issue one
Interference is always a major problem in wireless networks. Because users of indoor networks are stationary or moving relatively slowly, they may encounter interference that lasts for longer periods than in a highly mobile environment, such as a moving car. There is a greater chance, therefore, of an indoor call being dropped.

Interference inside a building depends on the relative position and distance of the base station to the user. In addition, the higher up in a building the user is, the more outdoor cell sites will be visible to the handset, increasing the probability of interference.

Controlling handoffs as described above is one way to reduce interference that arises from the outdoor environment. Other methods unique to the wireless technology can be used. For example, in TDMA networks, co-channel and adjacent-channel interference can be reduced by optimizing handover parameter settings to deny call attempts when the timing advance or alignment values are outside the accepted window for outside sites. This action forces the handset to reselect from the indoor network channels for service.

In CDMA networks, pilot number offset interference (co-PN interference) can be reduced by allocating a subset of PNs for indoor use only or by using a second carrier frequency dedicated to the indoor network.

Trends
Although many service providers have been slow to deploy indoor networks, they are starting to look more seriously at the need, particularly in areas where many users congregate and system capacity is strained. If service providers can realize benefits through additional subscriber usage or reduce churn by maintaining quality of service, then they will put in the necessary infrastructure.

In some cases, zoning restrictions on cell sites or excessive interference in the outdoor environment make an indoor RF network preferable. In the long run, data services are going to demand a better RF signal, and indoor systems will undoubtedly be required to deliver guaranteed data rates, particularly in high traffic areas such as airports and shopping malls.

Testing IS required
Testing is an integral part of designing, deploying and ensuring the ongoing operation of wireless networks. It supports all aspects of wireless engineering, from simple verification of data to the complex processes of system design and optimization.
About the author
John Catlin is regional manager of Agilent Technologies’ Wireless Network Services Division He manages Agilent's wireless network services organization for the Eastern U.S. region, which provides RF, fixed network, in-building and competitive benchmarking services to wireless network service providers and network equipment manufacturers. Tom Snyder is product planner of Agilent Technologies’ Wireless Network Solutions Business Unit. He is responsible for the long-term planning of Agilent's network optimization products. He works closely with customers and internal R&D teams to identify and develop future hardware and software products for Agilent.

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