Measurement Journal Issue 6

Growing capacity by increasing cell numbers Today there are approximately 1,000 subscribers per macro base station. Reducing this ratio has historically been the way system capacity has grown to meet demand. However, it seems evident from operators that making more than a token increase in macrocell density is not economically viable and thus the primary growth mechanism that has served us since wireless began seems to be nearing its end. There are ongoing efforts to deploy picocells and in-building systems but these too have practical limits. Breaking through to the next 10x or 100x of capacity growth means a dramatic increase in cell numbers is required — but the current centrally-managed deployment model will not scale due to costs and environmental factors such as planning and site availability. The time now seems right for the home base station or femtocell. With a femtocell in every second home it is possible to imagine a 100x growth in cell numbers compared to the current macrocellular model. With this femtocell assumption, a comparison of the capacity potential of the three axes in the capacity model from today through 2015 is shown in Figure 4. It is interesting to note that the outlook for capacity growth is much like the previous 50 years, with cell number upside being 100x more signiﬁcant than growth in either spectrum or efﬁciency. much change in the projected 2x spectrum growth through 2015, which will be available for 3G as well. Next we have efﬁciency, which is the focus of most of the study into 4G, but as we have seen the targets are very challenging and the upside remains low. Finally, regarding the number of cells, there were some encouraging discussions at the Shenzhen workshop on femtocells, although this is not currently seen as a major 4G initiative. For this reason it is perhaps fortuitous that 3GPP is already standardizing femtocell technology for both UMTS and LTE. The signiﬁcance of this cannot be underestimated since the potential upside from a femtocell deployment will address both the capacity and coverage limitations of current systems, plus the better radio conditions experienced in hotspot femtocell environments go hand in hand with delivering higher data rates. Femtocells: Enabling mobile broadband? Co-channel, self calibrated HNB Tx power 1 0.9 0.8 0.7 0.6 CDF 0.5 0.4 0.3 100 100 0.2 0.1 0 0 2 4 6 8 10 12 14 All UEs average throughput (bps) 16 18 Growth potential 10 24 HUEs + 10 MUEs/cell, 1 Rx 34 MUEs/cell, no HNBs, 1 Rx 3 2 1 Figure 5. Average throughput per user with and without femtocells Efficiency Spectrum Number of cells Figure 4. Capacity growth potential 2008 through 2015 How well are the 4G requirements addressing the need for capacity growth to match the demand from higher peak-data rates? Taking spectrum ﬁrst, this will always be mired in the slow-moving politics of international regulation. There are no expectations that the existence (or absence) of 4G will make The potential of femtocells is illustrated in Figure 5. This data was presented in June 2008 at 3GPP RAN WG4 as part of a femtocell study that included a simulation of user data rates with and without femtocells.7 The air interface is 5-MHz HSDPA using a single receiver with equalizer, 64QAM and 15 codes. For the macrocell case (blue trace), 34 UEs are evenly distributed across the cell and the median throughput is 40 kbps with the peak at 400 kbps. When the 96 femtocells are enabled, 24 UE choose to switch to the femtocells, leaving only 10 UE on the macrocell. Agilent Measurement Journal 58

Table of Contents Feed for the Digital Edition of Measurement Journal Issue 6

Measurement Journal Issue 6 Using a Few Words to Convey a Deeply-Held Spirit Charting a Unique Path to Technology Innovation Contents Announcing First Commercial GC/MS Metabolites Library Assessing Nonlinear Behavior Testing Combines Form and Function Testing Multiplay Networks Higher Sensitivity LC/MS Easing Military Radio Test Stepping Up Calibration Accuracy Increasing Spectrum Analyzer Bandwidth 3GPP Tool Supports TS 36 Standards The Olympic Story Spotlights Agilent's Continuing Contribution to Technology Innovation Ensuring a Level Playing Field in Competitive Sports GPS: Coming of Age Resolving Design Issues in HSPA Mobile Devices Achieving Accurate Results with Oscilloscope-Based Jitter-Analysis Software RF Handheld Testers Guarantee Traffic Stability Under Olympic-Sized Stress Conditions Utilizing LAN-Based Instrumentation to Measure Total Harmonic Distortion in Remote Facilities IMT-Advanced: 4G Wireless Takes Shape in an Olympic Year EPO Doping: A Speed Engine, Turbo-Charged by Chemistry

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