Further Enhanced ICIC (FeICIC)

FeICIC LTE-AdvancedGuest post by Faris Alfarhan*

In an earlier post, R10-LTE enhanced inter-cell interference coordination (eICIC) techniques for heterogeneous networks were discussed, along with the concept of small cell range expansion. The purpose of cell range expansion is to offload more traffic from macro cells to small cells and hence achieve larger cell splitting gains. By adding a cell selection bias, the service area of small cells increases and more users are offloaded to small cells. The need for heterogeneous networks interference management schemes stems from the fact that users in the small cell range expansion area are vulnerable to stronger interference signals than useful signals from the associated serving small cell. In the previous post, it was explained how time domain partitioning based eICIC schemes – known as Almost Blank Subframes (ABS) – could be used to control the interference on the data channels in the range expansion region. Further, carrier aggregation based techniques – known as Cross Carrier Scheduling – could be used to control interference on the control channels (such as the PDCCH, PCFICH, and PHICH channels). However, R10 eICIC schemes did not address interference control on cell-specific reference signals (CRS), which cannot be blanked in order to ensure backward compatibility with R8 and R9 UEs. In this post, R11 improvements to eICIC schemes are discussed, along with the shortcomings of R10 eICIC schemes. First, the concept of Reduced Power Almost Blank Subframes (RP-ABS) is explained along with its advantages over ABS. I then discuss the R11 techniques of Further enhanced ICIC (FeICIC) to control the interference on CRS resources. Read more of this post

Should Small Cells Be Deployed In Their Own Spectrum Band?

Small cells raise a number of practical implementation questions which are yet to be resolved. One such question is whether small cells should operate in the same frequency band as the macrocell layer (co-channel deployment), or on a different frequency band. The question has profound implications to operators, vendors, and to regulators alike.

To clarify, recall that in co-channel small cell operation interference between the macrocell and small cell layers limit the capacity gain of small cells. The benefit from small cells is realized when they are placed in traffic hot spots whose location must be identified (which is a challenge in itself). As LTE technology matures with advanced releases, techniques such as ‘Almost Blank Frame‘ are introduced to manage interference whereby a layer temporarily ceases operation to reduce interference to the second layer as shown in Figure 1. These techniques largely trade off some capacity for lower interference (but not network capacity: network capacity would still increase because small cells are added).  Using a different frequency band for small cells provides yet higher capacity because the different layers are separate networks. Read more of this post

Unleashing the Power of HetNets: Interference Management Techniques for LTE-Advanced Networks

In my earlier blog post, The Hype & Reality of Small Cells Performance, I provided a qualitative review of small cell performance and discussed interference scenarios that limit performance. Perhaps the most defining problem of small cell deployments is the large transmit power imbalance between the macrocell and the small cell (~20-30 dB) which increases the potential of uplink and downlink interference thereby limiting the ‘cell-splitting gain.’ As interference is the culprit in limiting performance, so managing it is at the crux of advanced LTE techniques. Fortunately, the LTE physical layer provides many levers to manage interference. Let’s recall that LTE is based on orthogonal division multiple access technology (OFDM) where orthogonal sub-carriers divide a wide channel bandwidth into multiple narrow frequency bands. Data is scheduled on sub-carriers which are assigned to users in the frequency and time domains (the basic unit of assigned sub-carriers is called a Resource Block). As we shall see, many of the interference management techniques are related to how the network assigns and manages its resources. But before we get into this, let’s have a look at range expansion which is a fundamental aspect of small cell deployments. Read more of this post