Carrier Aggregation and the Road to Cognitive Radio and Superwide Spectrum

Carrier AggregationOften, the least hyped technologies are the most effective, get the widest adoption, and have the greatest impact. Carrier aggregation is one such technology that I don’t think it received its fair share of attention. LTE did bring a number of new features that were not available in 3G, such as MIMO. But MIMO was already deployed in other technologies including both Wi-Fi and WiMAX. Carrier aggregation on the other hand developed by the requirement to achieve higher data rates in LTE network. True channel bonding is a feature of Wi-Fi, but it applies to adjacent channels. Carrier aggregation on the other hand combines distinct channels in different bands. From that perspective, I am not aware of any wireless technology that has implemented carrier aggregation. Read more of this post

On LTE-Advanced and Carrier Aggregation

LTE-AdvancedNews of LTE-Advanced is making headlines. SK Telecom aggregated two 10 MHz carriers in 800 and 1800 MHz to achieve 150 Mbps downlink throughput with a version of the Samsung Galaxy S4 handset built upon Qualcomm’s Snapdragon 800 SoC. Verizon announced that its LTE network is nearly complete and suggested carrier aggregation (CA) is the next step. AT&T on the other hand has plans to use carrier aggregation over its 700 MHz unpaired lower D and E blocks. 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