3.3 The Indoor UMTS/HSPA Challenge
When providing radio coverage for mobile users inside buildings, you are facing several radio planning challenges. It is mainly these challenges that motivate the need for indoor coverage solutions. Radio planners with indoor GSM planning experience need to be very careful not to apply all the radio planning strategy gained on GSM when designing indoor UMTS/HSPA solutions. If you are not careful, you will make some expensive mistakes and compromise high-speed data performance, as well as the business case for these indoor solutions.
3.3.1 UMTS Orthogonality Degradation
The UMTS RF channel efficiency is sensitive to degradation of the ‘RF environment’, typically caused by multipath reflections. Without going into mathematical details, the efficiency of the UMTS RF-channel is expressed using the term ‘orthogonality’. The higher the orthogonality of the radio channel is, the higher the efficiency of the radio link is.
The Data Efficiency on the UMTS Channel
The same 5 MHz (3.84 Mcps) UMTS RF channel can in some cases carry high data rates, in excess of 2 Mbps, provided that the users are in line-of-sight to the serving cell, and only if a minor portion of the signal is reflected energy. This is the typical indoor scenario, with a dedicated indoor coverage solution. In that case the orthogonality can be as high as 0.85–0.90, so the channel is very efficient in carrying high-speed data efficiently (as shown in Figure 3.4).