New Spectrum Usage Paradigms for 5G

Sometime back I wrote a post that talked about Dynamic Spectrum Access (DSA) techniques for Small Cells and WiFi to work together in a fair way. The Small Cells would be using the ISM bands and Wi-Fi AP's would also be contending for the same spectrum. For those who may not know, this is commonly referred to as LTE-U but the correct term that is being used in standards is LA-LTE, see here for details.

IEEE Comsoc has just published a whitepaper that details how the spectrum should be handled in 5G to make sure of efficient utilisation. The whitepaper covers the following:

Chapter 2 – Introduction, the traditional approach of repurposing spectrum and allocating it to Cellular Wireless systems is reaching its limits, at least below the 6GHz threshold. For this reason, novel approaches are required which are detailed in the sequel of this White Paper.

Chapter 3 - Spectrum Scarcity - an Alternate View provides a generic view on the spectrum scarcity issue and discusses key technologies which may help to alleviate the problem, including Dynamic Spectrum Management, Cognitive Radios, Cognitive Networks, Relaying, etc. 

Chapter 4 – mmWave Communications in 5G addresses a first key solution. While spectrum opportunities are running out at below 6 GHz, an abundance of spectrum is available in mmWave bands and the related technology is becoming mature. This chapter addresses in particular the heterogeneous approach in which legacy wireless systems are operated jointly with mmWave systems which allows to combine the advantages of both technologies. 

Chapter 5 – Dynamic Spectrum Access and Cognitive Radio: A Current Snapshot gives a detailed overview on state-of-the-art dynamic spectrum sharing technology and related standards activities. The approach is indeed complementary to the upper mmWave approach, the idea focuses on identifying unused spectrum in time, space and frequency. This technology is expected to substantially improve the usage efficiency of spectrum, in particular below the 6GHz range. 

Chapter 6 – Licensed Shared Access (LSA) enables coordinated sharing of spectrum for a given time period, a given geographic area and a given spectrum band under a license agreement. In contract to sporadic usage of spectrum on a secondary basis, the LSA approach will guarantee Quality-of-Service levels to both Incumbents and Spectrum Licensees. Also, a clear business model is available through a straightforward license transfer from relevant incumbents to licensees operating a Cellular Wireless network in the concerned frequency bands. 

Chapter 7 – Radio Environment Map details a technology which allows to gather the relevant (radio) context information which feed related decision making engines in the Network Infrastructure and/or Mobile Equipment. Indeed, tools for acquiring context information is critical for next generation Wireless Communication systems, since they are expected to be highly versatile and to constantly adapt. 

Chapter 8 – D2DWRAN: A 5G Network Proposal based on IEEE 802.22 and TVWS discusses the efficient exploitation of TV White Space spectrum bands building on the available IEEE 802.22 standard. TV White Spaces are indeed located in highly appealing spectrum bands below 1 GHz with propagation characteristics that are perfectly suited to the need of Wireless Communication systems. 

Chapter 9 – Conclusion presents some final thoughts. 

The paper is embedded as follows:

Novel Spectrum Usage Paradigms for 5G from Zahid Ghadialy

'Real' Full Duplex (or No Division Duplex - NDD?)

We all know about the two type of transmission schemes which are FDD and TDD. Normally, this FDD and TDD schemes are known as full duplex schemes. Some people will argue that TDD is actually half-duplex but what TDD does is that it emulates a full duplex communication over a half duplex communication link. There is also a half-duplex FDD, which is a very interesting technology and defined for LTE, but not used. See here for details.

One of the technologies being proposed for 5G is referred to as Full Duplex. Here, the transmitter and the receiver both transmit and receive at the same frequency. Due to some very clever signal processing, the interference can be cancelled out. An interesting presentation from Kumu networks is embedded below:

Full Duplex Radios in 5G from Zahid Ghadialy

The biggest challenge is self-interference cancellation because the transmitter and receiver are using the same spectrum and will cause interference to each other. There have been major advances in the self-interference cancellation techniques which could be seen in the Interdigital presentation embedded below:

Potential of Full Duplex for Future Wireless Systems from Zahid Ghadialy

Whitespace Spectrum Management Issues

BT has been conducting a "White Space" trial in Isle of Bute, UK. Initial report suggests that the results are not very impressive. The following is from ISP Review:

Early feedback from BT’s trial of ‘White Space‘ (IEEE 802.22) wireless broadband technology on the Isle of Bute suggests that the service, which delivers internet access by making use of the unused radio spectrum that exists between Digital TV channels, still has a lot of problems to overcome, not least in terms of its sporadic performance.

In theory the 802.22 specification suggests that download speeds of up to 22Mbps per channel (Megabits per second) could be possible and some UK trials claim to have reached around 16Mbps, which is incidentally a long way off the UK’s chosen definition for superfast broadband (24Mbps+).

But separate reports from both PC Pro and the BBC today found that the service, which is complicated to deliver due to the ever changing spectrum and the risk of causing interference to DTV services, could struggle to deliver its top speeds.

At present BT’s implementation claims to be offering speeds of up to 10Mbps per channel, which will soon be upgraded to 15Mbps, but this reduces down to a maximum of just 4Mbps when 6km away from the transmitter. New tests at various points on the Isle of Bute showed speeds varying between just 1.5Mbps and 6Mbps (the latter was recorded within sight of BT’s mast).
In fairness White Space solutions are designed to target the last 10% of the UK where the government has so far only committed to a minimum download speed of just 2Mbps for all (Universal Service Commitment), which is a very low target. In addition White Space tech appears to deliver strong upload speed that is, in some cases, symmetrical. That makes it good for video conferencing and other upload dependent tasks.



As Fierce Broadband Wireless suggests, the low speeds could also be due to pre-standard gear that will just improve as time goes on.

The main reason for using this shared whitespace spectrum is due to the fact that the total amount of spectrum is limited and we want to make use of every available free spectrum to increase capacity of the overloaded networks.

Michael Fitch from BT recently spoke in our Cambridge Wireless Small Cells SIG event. The slide from his presentations neatly lays out the vision for shared spectrum.

In theory, even though this looks simple, in practice managing the database is a challenge by itself. The embedded slides below (Page 17 onwards) show the problems and the complexity associated with the database.

Spectrum sharing issues for small cells

View more presentations from Zahid Ghadialy

Time will tell how efficient and practical using whitespaces is.

Explaining the Alcatel-Lucent 'lightRadio' concept

Cognitive LTE Small Cell Networks

View more presentations from Zahid Ghadialy

Cognitive radio – the way out of spectrum crunch?

Another presentation from the Cambridge Wireless Event on Avoiding Cellular Gridlock. One of the ways suggested in the discussions with regards to the 'Geo-location database' (see slide 12) is that they could also be done using Smart Grids. Though it sounds simple in theory, practically we may never see that happen and that would not be due to any technical reasons.

Cognitive radio – the way out of spectrum crunch?

View more presentations from Zahid Ghadialy

Locating Wireless Devices Where GPS May Not Be Available

Some of you may have read my earlier posts on stealing spectrum via Femtocells and using Femtocells abroad illegally. This presentation tries to answer one such problem on how do you find the location where GPS cannot be used. This could also be used in case of Cognitive Radios. See my old blog entry here.

OFCOM Locating Wireless Devices where GPS may not be available

View more presentations from Zahid Ghadialy.

4G Mobile Network & Applications

4G Mobile Network & Applications

View more presentations from Kuncoro Wastuwibowo.

Ericsson Presentation: Cognitive radio in Europe

Cognitive radio in Europe [John Holland]

View more presentations from Keith.

SDR: Today and Future

I also got an opportunity to attend the SDR briefing in LTE World Summit. There were many interesting presentations including one titled "SDR in Mobile Devices" by Thierry Dubois, SDR Market Analyst, IMEC, Belgium. Infact last year I blogged about SDR from Imec presentation as well. The following is an extract from Thierry's presentation:

The key benefits of SDR are as follows:

• Reducing the Bill Of Materials (BOM)
• Lower development costs
• Facilitate better reuse of intellectual property (IPR)
• Possibility to upgrade products already in the field
• Enabler of the Cognitive Radio vision

There are three main areas where SDR's are required but some problems exist as can be seen from the diagram above.

• Flexibility is the key for baseband. Some of the common signal processing blocks may not be reusable. This means that though some protocols can easily be defined for a particular baseband, others may not be possible for that baseband. Good progress is still being made though on this front.
• Reconfigurable RF is some way away, further down the road.
• The biggest challenge is the antenna interface for which no proper solution exists. Some solutions being worked on right now include MEMS based solution, Carbon nanotubes, Special ceramic materials, etc.

The next step after SDR is cognitive radio (CR). The main advantage for using CR would be because spectrum is over-allocated but under-utilised. There are lots of white spaces in the spectrum that could be utilised by devices intelligently of their own.

Cognitive Radios are defines as: A radio that can autonomously change its parameters based on interaction with, and possibly learning of, the environment in which it operates. Through appropriate radio resource management, such a cognitive radio should make flexible and efficient use of network/spectrum resources.

CR would consist of Intelligent Sensing hardware and Intelligent Sensing Algorithms. There are two types of CR being considered:

• Opportunistic Radio: A radio that co-exists with other systems using the same spectrum. E.g., White Space Devices
• Smart Reconfigurable Radio Systems: A radio that makes flexible and efficient use of network/spectrum resources across heterogeneous environments. Seamlessly roaming possible on different networks, countries, frequencies, etc. It requires true paradigm shift i.e., spectrum liberalization

An Introductory paper on SDR is available on Bitwave Semiconuctor website.

Cognitive radio

Cognitive radio (CR) is a newly emerging technology, which has been recently proposed to implement some kind of intelligence to allow a radio terminal to automatically sense, recognize, and make wise use of any available radio frequency spectrum at a given time. The use of the available frequency spectrum is purely on an opportunity driven basis. In other words, it can utilize any idle spectrum sector for the exchange of information and stop using it the instant the primary user of the spectrum sector needs to use it. Thus, cognitive radio is also sometimes called smart radio, frequency agile radio, police radio, or adaptive software radio,1 and so on. For the same reason, the cognitive radio techniques can, in many cases, exempt licensed use of the spectrum that is otherwise not in use or is lightly used; this is done without infringing upon the rights of licensed users or causing harmful interference to licensed operations.

The only difference with SDR (Software Defined Radio) is that a cognitive radio needs to scan a wide range of frequency spectra before deciding which band to use, instead of a predefined one, as an SDR terminal does. One of the most important characteristic features of an SDR terminal is that its signal is processed almost completely in the digital domain, needing very little analogue circuit. This brings a tremendous benefit to make the terminal very flexible (for a multimode terminal) and ultrasmall size with the help of state-of-the-art microelectronics technology.

More Information at:

http://www.technologyreview.com/read_article.aspx?ch=specialsections&sc=emergingtech&id=16471

http://www.ece.gatech.edu/research/labs/bwn/CR/Projectdescription.html

http://en.wikipedia.org/wiki/Cognitive_radio