Tuesday, March 29, 2016

Commentary: Only Millimeter Wave MMW (E-Band) - 70/80GHz Can Drive QoS For LTE Advanced Deployments in Nigeria

The next turning point in LTE’s exciting journey came on October 21, 2010 when the ITU issued a press release which qualified LTE Advanced (LTE-A) and WiMAX 2 as meeting the requirements for 4G standard. Consequently, 3GPP, the international body that developed the wideband CDMA-based UMTS 3G standard, defined LTE as a 3.9G technology and designated LTE-A as the real 4G technology. LTE-A is going to be built on the prior OFDM/ MIMO-based LTE architecture to further increase data rate and subsequently defined in 3GPP Releases 10 and 11.
The LTE-A standard ( expected to offer peak rates up to 1 Gbit/s fixed speeds and 100 Mb/s to mobile users) will be forward and backward compatible with basic LTE, meaning that LTE handsets will work on LTE-A networks, and LTE-A handsets will work on standard LTE networks. That makes LTE a stepping stone to the much-higher-capacity LTE-A systems. The deployment of LTE-A is expected in 2014 and beyond. The LTE-A standard promises three times greater data speeds than LTE. It boasts five major features: carrier aggregation, increased MIMO, coordinated multipoint transmission, heterogeneous network (HetNet) support, and relays. Carrier aggregation combines up to five 20-MHz channels into one stream to increase data speed, making possible a peak downlink data rate of 1 Gbit/ s and uplink data rate of 500 Mbit/ s. Next, while the standard LTE defines MIMO configurations of up to 4x4 arrangement, LTE-A extends that to 8x8 stream with support for two transmit antennas in the handset. Third,cooperative MIMO— is a set of techniques using different forms of MIMO and beamforming to improve the performance at cell edges. Finally, LTE-A defines a virtual base station type called relay station. Relays use repeater stations to help coverage in selected areas, especially indoors where most calls are initiated. The five key technology features of LTE-A system are carrier aggregation, increased MIMO, coordinated multipoint transmission, heterogeneous network support, and relays. Image credit: EE Catalog
The first critical juncture in mobile industry’s quest for multifold increase in capacity and flexibility of cellular networks came with the realization that the big tower-based macro-umbrella networks that fueled two decades of voice services weren’t going to cut it in a data-centric world. So mobile carriers and their infrastructure vendors began designing new types of small cells and base stations intended to deliver intense levels of bandwidth over limited areas. 
These small cell deployments— pico, micro, metro, femto, etc.— are to evolve into the new heterogeneous network, or HetNet, which will transform cellular systems from coverage- to capacity-focused systems. This implies that the upcoming broadband mobile networks will have hundreds of thousands if not millions of cells. LTE became a driving force behind the small-cell movement. In retrospect, mobile operators could have created far more capacity if they deployed smaller cells, reusing the spectrum they had to the nth degree. But they couldn’t build the density of cells necessary to support the demands for mobile data. It was a hard feat to pull off because at any time, when two signals used the same frequency in the same space, there would be interference. So, for several years, the mobile industry had been trying to figure how to mitigate that interference. That’s why it had taken so long to convert an ordinary picocell into a true small cell. Now, instead station, typically designed for use in a home or small business.
Typically, the range of a standard macrocell is up to 35 kilometres or 22 miles; a microcell is less than two kilometers wide; a picocell is 200 meters or less; and a femtocell is on the order of 10 meters. At first, small cell network will function much like an extension of the large cell counterparts. The network will pass mobile users from big cell to small cell and vice versa. However, the key difference is that when mobile users occupy the small cell, they will have a lot more bandwidth at their disposal. Mobile devices will be able to link to multiple cells simultaneously, and the same signals that once interfered with one another will reinforce one another creating an even more powerful connection. 
The high-capacity Wi-Fi networks will also get layered in, creating a heterogeneous network in which mobile devices can establish multiple simultaneous connections using multiple radio technologies. Apparently, that boils down to an awful lot of bandwidth. The two main deployment scenarios for small cells are in rural areas with poor or no indoor coverage, probably using co-channel deployment, and in dense areas to provide high data rates and capacity. 
Femtocells and other microcell schemes are an integral part of the LTE deployment strategy. With revenue per bit falling, costs for deployment must be kept to a minimum while ensuring that the network is operating to its greatest efficiency. In 2013, the U.S. mobile carriers were getting ready for their first small cell deployments with an aim of implementing multi-technology heterogeneous networks. Networking equipment maker Cisco estimates that Wi-Fi and femtocells will handle nearly half of all mobile traffic by 2017.
Cellular networks have always occupied frequencies lower on the spectrum, where carrier waves tens of centimeters long— hundreds of megahertz— pass easily around obstacles and through the air. But this coveted spectrum is now heavily used, making it difficult for mobile phone operators to acquire more of it.
At the same time, many 4G networks have just about reached the theoretical limit on how much data they could squeeze into a given amount of spectrum. So, wireless engineers are now looking toward higher frequencies, where radio use is lighter. Here, regulators can free as much as 100 GHz of millimeter-wave spectrum for mobile communications— about 200 times what mobile networks use in 2013. Wireless systems that use millimeter waves already exist for fixed, line-of-sight transmissions.
Moreover, because a single millimeter-wave antenna has a small aperture, it needs more power to send and receive data than is practical for cellular systems. Beamforming is a signal processing technique that is used to direct the reception or transmission of a signal in an array in a chosen angular direction. Each user's signal is transmitted and received by the base station only in the direction of that particular user; that drastically reduces the overall interference in the system and improves the system capacity.
Therefore, not only could millimeter-wave technology merit for those small cells,it could also provide a simple, inexpensive alternative to backhaul links, which connect cellular base stations to mobile operators’ core network. Today millimeter-wave deployments in Nigeria can provide up to 10GBps with a single ODU. Deploying a 2+0 configuration provides 20Gbps as well as a failover if one link goes down.
The small cells would be mounted on street poles, building walls and every form of urban fixture where access to cable or fiber isn’t readily available and the cost of laying fiber is prohibitive. LTE requires fat backhaul pipes and millimeter wave technologies can provide both the reach and capacity at the right prices for the HetNet backhaul.
Millimeter wave transmission systems suit to small cell backhaul for two reasons. First, it is relatively easy to get licenses for big blocks of millimeter wave spectrum, which will allow mobile operators to deploy large backhaul pipes of over 1 Gbit/ s. While a single small cell might not need that much capacity, the complexity of HetNets will require daisy-chaining many small cells together, each cell passing its load down the line. The final backhaul link in such a mesh or chain could end up handling dozens of cells worth of traffic before it dumps the data onto a core fiber network. 
Second, by definition, the HetNet will be composed of densely packed cells in urban environments, meaning millimeter wave won’t have to travel far between hops. Millimeter wave communications technology is winning merits in the evolving 5G domain because small cells architecture and HetNets are inherently suitable for millimeter wave-based network configuration. 
In Lagos, a densely congested city of more than 20mil, MMW can cost effectively provide backhaul for LTE to achieve high QoS. It will also be a cost effective means for bringing access to non/underserved population estimated to be around 40mil.  In addition, apart from MMW for LTE, overall increase of QoS  can be realized if more carriers and operators would offload some of their MW transmissions to MMW.  
NCC anticipated the benefits that millimeter-wave technology would provide by releasing a "light licensing" model with low-cost license fees as well as a simple application process soon to be online.  The regulator also envisioned that the millimeter-wave spectrum would provide relief to the overuse of MW often causing interference.  As more operators and ISPs understand the many benefits of this spectrum, QoS will quickly rise for Nigerian subscribers.   
*Ken Spann contributed this from Lagos with credits for content given to Ahmad, Majeed (2013-12-17). Essential 4G Guide: Learn 4G Wireless In One Day (Smartphone Chronicle) Majeed Ahmad Kamran. Kindle Edition.
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PIX: Ken Spann

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