Cloud RAN vs. Picocells: The Need for Integrative Approach in Next Generation Network Design.

Picocell vs. Cloud RANWhen it comes to deciding on deploying small cell base stations, one is faced with a few options. One option is based on cloud RAN architecture with remote radio heads connected through optical fiber to a central base station housing the baseband processing. A second option is that of a compact base station which includes both the radio frequency and baseband processing functions. The compact base station is connected to the core network by a number of different backhaul technologies.

The availability of low cost fiber is a gating factor in deploying cloud RAN architecture. Remote radio heads require very high capacity links to support modern air interface features such as multiple antennas for MIMO. CPRI and OBSAI interfaces run at between 3 and 6 Gbps depending on the number of supported antennas. The compact base station on the other hand requires much lower capacity for backhaul – on the order of tens to over a hundred Mbps.  Low backhaul throughput requirements should translate into lower deployment cost to the advantage of compact base stations. Read more of this post

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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

The Hype and Reality of Small Cells Performance

Heterogeneous networks (HetNets) consist of large (macro) cells with high transmit power (typically 5 W – 40 W) and small cells with low transmit power (typically 100 mW – 2 W). The small cells are distributed beneath the large cells and can run on the same frequency as the large cell (co-channel), or on a different frequency. As an evolution of the cellular architecture, HetNets and small cells have gained much attention as a technique to increase mobile network capacity and are today one of the hot topics in the wireless industry. Many of the initial deployments of small cells are of the co-channel type. Standards such as LTE have focused on incorporating techniques to improve the performance of co-channel deployments in earlier releases of the technology standard leaving the handling of multi-frequency deployment type to later releases. In all, operators today have multiple options of small cell deployment scenarios, operational techniques and technology roadmaps to choose from. Read more of this post

More and More Small Cells, But Where’s the Gain?

Small Cell StrategySmall cells are meant as a solution to address the explosive growth in mobile data services, right? Well, the answer is: it depends! They can be a solution under certain conditions, but not always. Yes, there could be situations where small cells add little if any gain. In fact, more than one operator mentioned to me little or even no gain in overall capacity increase by their small cell pilot projects. So what’s happening, and why can we run into situations where small cells don’t deliver on their promise? Read more of this post

TD-LTE and the Hype Cycle: Where’s the Business Opportunity?

As a new wave of hype is building around TD-LTE, I wonder what the fuss is all about. For certain, TD-LTE is not a groundbreaking technology – it comes many years after WiMAX and quite a few after its older FD-LTE sibling. But what intrigues me most is the business model for TD-LTE and especially the dilemma of the TDD spectrum holder: what is a winning business model that maximizes the value of my operation and company? Without such a model, TD-LTE will be yet another technology toddler that never makes it to adulthood. Read more of this post

Use Cases for the 2.5/2.6 GHz Spectrum: Macro or Micro/Pico Cells?

Should operators deploy a macro or micro cellular architecture in 2.5 GHz band? This is not a trivial question particularly for an incumbent wireless operator that already holds spectrum in lower spectrum bands. The same can be said of Greenfields looking to capitalize on the exponential demand for wireless data services. Read more of this post