28 September 2016
Why millimeter wave for telecommunication infrastructure?

Why millimeter wave?
Microwave[2] is reaching its maximum capacity and there is not enough available bandwidth for microwave links to backhaul all the data from the base stations/access point (BTS/AP). Traditional microwave bands are, due to regulatory reasons, often limited to bandwidth of 56 to112 MHz for each channel available for a point to point backhaul link. Hence microwave links offer typically up to 1 Gbps using very high modulation schemes like 4096-QAM[3]. If the modulation in the next generation of microwave links would be increased to 8192 QAM, that would increase capacity to 13 bits per symbol, which is an increase of a mere 8%. Therefore, it is quite clear that microwave links for point to point has reached its limits. To understand which category of backhaul a BTS requires, we make a very rough estimate for LTE Category 4 and LTE-Advanced Category 6 use. LTE Category 4 devices sold today allowing peak downlink speeds of up to 150 Mbps, this would give you less than 10 concurrent users on one 1 Gbps link. For LTE-Advanced Category 6, devices will push these speeds even higher, supporting up to 300 Mbps downlink that would suggest only 3-4 concurrent users on a 1 Gbps link. Without going into details about macro cell and small cells, we can clearly see that the total speed for the backhaul link needs to increase and even more so for 5G. On top of this, millimeter wave solution also offers the possibility to develop smaller antennas with decreased cost as well as size of the final product, which are very important aspects for all telecommunication infrastructure.

Which technology can support 10x (or even in the future100x) more speed? Millimeter waveis one option, fiber is another one. Focusing on millimeter wave, in the US FFC now offer V-band (57-71 GHz) with 14 GHz of available bandwidth and E-band (71-76 GHz, 81-86 GHz) offer 10 GHz bandwidth, in these bands it is common to use up to 2 GHz bandwidth for each link, i.e. 20 times more bandwidth than microwave can offer. On top of this, V-band being license free in the US, creating obvious cost advantages for the operators compared to the traditional microwave bands. Using 2 GHz bandwidth and 128 QAM modulation, you will ideally achieve at least 10 Gbps. This is not only theory, the technology is already available and proven for this kind of millimeter wave links. In future solutions, even higher data speeds of 20, 50 and 100 Gbps can be supported by more robust millimeter wave products supporting wider bandwidths and advanced MIMO configurations.

Based on this, Sivers IMA has identified several interesting use cases for millimeter wave with a focus on telecom infrastructure: macro cell backhaul, small cell backhaul, Remote Radio Head (RRH) fronthaul for C-RAN, Wireless gigabit to home (GBTH), mesh point to multipoint networks and Video surveillance backhaul applications. These use cases and application domains are described in detail below. There are, of course, several other use cases for millimeter wave for telecom infrastructure, for example mobile access for 5G, but that will be addressed in future blog post.

Macro cell backhaul 
Macro cells have been the preferred choice for cellular networks, for example 2G, 3G and 4G GSM/LTE networks have traditionally used macro cell since they cover a large area using sub 6 GHz band for communication between the handset (e.g. smart phone) and the BTS macro site. Common backhaul have been microwave, copper and fiber. The total market for microwave backhaul is around 5.000 MUSD per year, which is equal to about 1-1.2 million units shipped per year over the last 10 years. Fiber usage for backhaul is estimated to double in size until 2019 according to ABI research. Due to the above mentioned limitations in microwave, we see a big need for millimeter wave solution for macro cells, which is confirmed by Ericsson estimating that 20% of the wireless backhaul will be E-band millimeter wave by 2020. E-band is well suited for longer hops, using high gain antennas and high output power and can today offer up to 10 Gbps speed.

Small cell backhaul 
Indoor small cells have been very successful over the last couple of years and are often connected using fixed line solutions. Outdoor small cells have been a market that has been less successful due to different hurdles connected to the total cost of owner ship (TCO) for a small cell, including lack of cost effective millimeter wave solutions. Applying low cost modems, radios and license free V-band (57-71 GHz) will however support a much lower TCO and hence support the uptake and densification of the mobile network. However, only time will tell if outdoor densification is going to be done via “traditional” small cells and/or Cloud-RAN solutions using Remote Radio Head (RRH). It is however very clear that to support the growing demand for data, densification of the mobile network needs to happen using millimeter wave, where the option will be V-band as point to point links or V-band mesh network using point to multi point links (see below for more on mesh networks).

RRH fronthaul for C-RAN
Cloud-RAN (C-RAN) is the proposed architecture for future cellular networks, sometimes defined as Centralized-RAN. In this architecture, the remote radio head (RRH) is separated from the baseband unit (BBU) by fiber or wireless millimeter wave links. As an example, digital baseband signals are carried to the RRH with a wireless millimeter wave link according the OBSAI standard or CPRI protocol. RRH will be much cheaper than a full small cell BTS, hence TCO will be even lower for the mobile operator than for a traditional small cell BST deployment. However, the backhaul requires low latency and the CIPR protocol carrying the digital baseband signals is very demanding, e.g. large bandwidth, high data speeds (5-10 Gbps) as well as low latency are required. Only millimeter wave links and fiber can offer this. If no fiber is available at the site, the cost for millimeter wave will be much less than digging new fiber as well as deployment time will be much shorter, hence C-RAN solutions will in many cases use millimeter wave to support the densification needed for bandwidth hungry applications. Hence, for LTE-Advanced Category 6 as well as 5G RRH based on C-RAN solutions, millimeter wave links will be a key enabler.

Wireless gigabit to home (GBTH)
In the US, there is a race to win the high speed residential internet market (also sometimes called: Gigabit to home, GBTH). For example, Google Fiber has been investing heavily in fiber deployment over many years. Recently Google Fiber halted[4] the roll-out of fiber and instead announced that also wireless millimeter wave links should be used. This is due to that fiber is more expensive and costly to deploy than the new “WiGig” wireless millimeter wave infrastructure that can be built based on the IEEE 802.11ad standard, which will be used as the Internet connection to the home. These links need to provide a minimum speed of 1 Gbps to be able to provide these speeds and links at low cost, Google and others need to use license free 60 GHz spectrum and low cost millimeter wave 802.11ad technology. Sivers IMA is developing “WiGig” wireless millimeter wave infrastructure solutions compliant with the IEEE 802.11ad standard, with a focus on providing a competitive edge on performance and robustness for this type of demanding datacom infrastructure solution. In our next blog we will share more details about what kind of technology this is and why it is superior compared to other technology.

Mesh point to multipoint networks 
Wireless mesh networks are typically a network with several nodes that can reach one or more nodes in the same network. Each node in a meshed network includes several modems and RFICs, e.g. in order to cover 270-360 degrees beam steering, 3-4 RFICs are normally needed. This type of networks is often very robust and offers true redundancy, which is very important for solutions having multiple wireless hops. We see a big interest in using both licensed free and licensed band for wireless mesh networks and low cost millimeter wave technology will be key to enable large volumes.

Video surveillance backhaul applications
When deploying 4K Ultra HD Video surveillance cameras you need high speed links. Millimeter wave wireless mesh networks or point to point network are well suited to support the rollout of these video surveillance cameras. 4K Ultra HD needs a lot of bandwidth and a quick rollout requires wireless infrastructure. Low cost and high speed millimeter wave backhaul technology will hence play a very important role in making this type of solutions work.

As you can see, based on the above use cases, there is a big need for high performance and high speed millimeter wave technology. With the knowhow and technology at Sivers IMA, we are convinced that we are well positioned to support the growing millimeter wave market with advanced and competitive products. In our next blog, we will share more details on how we have chosen the right technology to be able to offer robust and reliable millimeter radios for the different use cases described above. 

Anders Storm
Sivers IMA

[1] Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2015–2020 White Paper

[2] Microwave bands are often referred to as 6-42 GHz

[3] 4096 QAM is equal to 12 b/symbol. The number of bits per symbol times the available bandwidth gives you roughly the maximum speed of the link (not including other technologies like XPIC, MIMO etc.)

[4] http://www.theverge.com/2016/8/15/12492890/google-fiber-wireless-plans-la-chicago-dallas