MU-MIMO (and DIDO)

Late last month a guy called Steve Perlman announced of a new technology called DIDO (Distributed-Input-Distributed-Output) that could revolutionise the way wireless transmission works and can help fix the channel capacity problem as described by Shannon's formula. A whitepaper describing this technology is available here.

I havent gone through the paper in any detail nor do I understand this DIDO very well but what many experienced engineers have pointed out is that this is MU-MIMO in disguise. Without going into any controversies, lets look at MU-MIMO as its destined to play an important part in LTE-Advanced (the real '4G').

Also, I have been asked time and again about this Shannon's channel capacity formula. This formula is better known by its name Shannon-Hartley theorem. It states:

C <= B log2 (1 + S/N)

where:

C = channel capacity (bits per second)

B = bandwidth (hertz)

S/N = Signal to Noise ratio (SNR)

In a good channel, SNR will be high. Take for example a case when SNR is 20db then log2 (1 + 100) = 6.6. In an extremely noisy channel SNR will be low which would in turn reduce the channel capacity.

In should be pointed out that the Shannon's formula holds true for all wireless technologies except for when multiuser transmission like MU-MIMO (or DIDO) is used.

Anyway, I gave a simple explanation on MU-MIMO before. Another simple explanation of what an MU-MIMO is as explained in this video below:

The picture below (from NTT) gives a good summary of the different kinds of MIMO technology and their advantages and disadvantages. More details could be read from here.

Click to enlarge

As we can see, MU-MIMO is great but it is complex in implementation.

Click to enlarge

Multiuser MIMO technology makes it possible to raise wireless transmission speed by increasing the number of antennas at the base station, without consuming more frequency bandwidth or increasing modulation multiple-values. It is therefore a promising technology for incorporating broadband wireless transmission that will be seamlessly connected with wired transmission in the micro waveband (currently used for mobile phones and wireless LAN, and well suited to mobile communications use), where frequency resources are in danger of depletion. Since it also allows multiple users to be connected simultaneously, it is seen as a solution to the problem specific to wireless communications, namely, slow or unavailable connections when the number of terminals in the same area increases (see Figure 9 above).

There is a good whitepaper in NTT Docomo technical journal that talks about Precoding and Scheduling techniques for increasing the capacity of MIMO channels. Its available here. There is also a simple explanation of MIMO including MU-MIMO on RadioElectronics here. If you want to do a bit more indepth study of MU-MIMO then there is a very good research paper in the EURASIP Journal that is available here (Click on Full text PDF on right for FREE download).

Finally, there is a 3GPP study item on MIMO Enhancements for LTE-Advanced which is a Release-11 item that will hopefully be completed by next year. That report should give a lot more detail about how practical would it be to implement it as part of LTE-Advanced. The following is the justification of doing this study:

The Rel-8 MIMO and subsequent MIMO enhancements in Rel-10 were designed mostly with homogenous macro deployment in mind. Recently, the need to enhance performance also for non-uniform network deployments (e.g. heterogeneous deployment) has grown. It would therefore be beneficial to study and optimize the MIMO performance for non-uniform deployments where the channel conditions especially for low-power node deployments might typically differ from what is normally encountered in scenarios considered so far.

Downlink MIMO in LTE-Advanced has been enhanced in Release 10 to support 8-layer SU-MIMO transmission and dynamic SU-MU MIMO switching. For the 8-tx antenna case, the CSI feedback to support downlink MIMO has been enhanced with a new dual-codebook structure aimed at improving CSI accuracy at the eNB without increasing the feedback overhead excessively. Precoded reference symbols are provided for data demodulation, allowing arbitrary precoders to be used by the eNB for transmission. In many deployment scenarios, less than 8 tx antennas will be employed. It is important to focus on the eNB antenna configurations of highest priority for network operators.

The enhancement of MIMO performance through improved CSI feedback for high priority scenarios not directly targeted by the feedback enhancements in Release 10, especially the case of 4 tx antennas in a cross-polarised configuration, in both homogeneous and heterogeneous scenarios should be studied.

MU-MIMO operation is considered by many network operators as important to further enhance system capacity. It is therefore worth studying further potential enhancement for MU-MIMO, which includes UE CSI feedback enhancement and control signaling enhancement. Furthermore, open-loop MIMO enhancements were briefly mentioned but not thoroughly investigated in Rel-10.

In addition, the experience from real-life deployments in the field has increased significantly since Rel-8. It would be beneficial to discuss the experience from commercial MIMO deployments, and identify if there are any potential short-comings and possible ways to address those. For example, it can be discussed if robust rank adaptation works properly in practice with current UE procedures that allow a single subframe of data to determine the rank. In addition the impact of calibration error on the performance could be discussed.

This work will allow 3GPP to keep MIMO up to date with latest deployments and experience.

Lobbying for more Spectrum

The following Video is prepared by Mobile Future which is a coalition in the US of some major companies and have been lobbying for increase in the availability of the Spectrum.

Patent Wars Part 2 - Who is suing whom

Continuing from the earlier post on the Patent Wars, here is a chart on who is suing whom.

Via: ReadWrite Mobile & Reuters

Patent Wars!

Patent wars has picked up force in the recent few months. Last week the Samsung Galaxy S2 Android phone was banned from the EU due to a suit from Apple but this ban has now been lifted. HTC has sued Apple over patents infringement and is asking for a ban in the US.

Patents are becoming more and more important. In June, Apple and Microsoft (once cut-throat rivals) teamed up with four other companies to pay $4.5 billion for the 6,000 patents held by the bankrupt Nortel Networks. This works out to $750,000 a patent. Google is now in the process of buying Motorola

NY Times report says:

Motorola Mobility in no small part because of its stockpile of 17,000 patents. The patent portfolio, some analysts estimate, could represent more than half of the value of the deal, or more than $400,000 a patent. If so, it was a relative bargain compared to the Apple and Microsoft aquisition of Nortel patents.

In the case of Motorola, Google was under pressure from its big handset partners, including HTC and Samsung, to protect them from patent-infringement suits based on their use of Google’s Android software. And Motorola has an impressive collection of mobile phone patents, a powerful weapon in patent negotiations.

Handset makers and mobile carriers are certainly hoping that Google’s purchase of Motorola will ease tensions in the smartphone market — a patent armistice among rival powers. Verizon on Tuesday welcomed the deal as a move that might well “bring some stability to the ongoing smartphone patent disputes,” John Thorne, senior vice president and deputy general counsel, said in a statement. Verizon Wireless, owned by the Vodafone Group and Verizon Communications, sells both Android-powered phones and iPhones.

In a recent blog post, David Drummond, Google’s chief legal officer, wrote that a modern smartphone might be susceptible to as many as 250,000 potential patent claims (see picture below), depending on how broadly those patents and claims were interpreted.

There was some interesting analysis on the Google Motorola deal by one Josh Pritchard in Quora:

Assuming Google would find value in the patent portfolio and not the operating businesses, an acquisition would presumably only make sense if Google had another partner (or partners), like HTC or Samsung, that wanted Motorola Mobility's operating businesses. If they could work out an arrangement with Google getting the patents and a partner (or partners) taking the other assets, then I'll argue that an acquisition could make a lot of sense based on a sum of the parts analysis.

Motorola Mobility has ~$3.2B in cash (~$170M are hiding as "cash deposits" on a separate line in the balance sheet, and are easily overlooked) with another $225M in additional payments from MSI still pending. They have $2.4B in deferred tax assets, though without reasonable expectations for operational profitability, they carry a $2.3B valuation allowance (again, easily overlooked). If the patents portfolio is worth anywhere near what Google [and Intel] bid on the Nortel patents, say $3.5B, then the sum of those parts is well over $11B in potential value. That's before assigning *any* value to the mobile and set-top operating businesses themselves.

But the operating businesses are almost certainly not worthless. They are set to generate ~$14B in revenue this year and the mobile business, with 41% Y/Y growth, is finally set to become profitable in Q4 of this year... if you believe the company's estimates. If a partner of Google's could reasonably expect to consume the operating businesses and then use their scale and/or superior supply chain to quickly bring them to even greater profitability, it's easy to imagine them being willing to pay at least some fraction of this year's revenue for the businesses, separate from the cash and tax assets. A multiple of .25X on this year's sales would be $3.5B. Seems low.

In total, that's in the neighborhood of $15B in value for a company that currently has a market cap under $7B. So, one might conclude that Google and its partner(s) could pay somewhere between those two numbers, providing a significant premium to market while still acquiring the assets below their fair value.

Of course, there are some restrictions on what MMI can do in its first 24 months as an independent entity, per the terms of the Tax Sharing Agreement documented in the 10-12B/A from the separation in January (when MOT became MSI and MMI). Per my understanding of those terms, if MMI takes actions that compromise the tax-free standing of the separation, as an outright acquisition might do, then they would be on the hook for any resulting tax liabilities. However, as the agreement states, "Though valid as between the parties, the Tax Sharing Agreement is not binding on the IRS" -- and, moreover, I believe there is quite a bit of leeway in terms of how an agreement could be structured in order to preserve the tax-free standing of the separation.

Whatever the case, a Twitter joke suggested that is people would want to retain jobs in Motorola, they better dress up as Patents and go to work.

Finally, patent pools is a good idea and can avoid lots of potential lawsuits and counter-suits. One such company very active in promoting a pool is Sisvel. A presentation from them in the LTE World Summit is embedded below.

Intellectual Property Rights (IPRs) vs.Standardization in theTelecommunications Arena: Clash of the Titans?

View more presentations from Zahid Ghadialy

Converged Mobile Offload Architectures

Converged Mobile Offfload Architectures

View more presentations from All About 4G

LTE Spectrum Strategies and Forecasts to 2016

LTE Spectrum Strategies

View more presentations from ThomasInforma

mHealth – Mobile Healthcare; consumer, doctors, healthcare providers, hardware and software tech enablers

The following is from a recent Mobile Internet SIG in the SV Forum.

You may want to get the presentations before listening to the video. Presentations available here.

4G Refarming Scenarios - Picture

Click on image to enlarge

From an old presentation of Qualcomm in the LTE World Summit 2010.

Self-Evolving Networks (SEN): Next step of SON

In a post last year, I listed the 3GPP features planned for the Self-Organising networks. Self-optimisation has been a part of the SON. It is becoming more of a common practice to refer to SON as Self-Optimising networks. A recent 4G Americas whitepaper was titled "Benefits of self-optimizing networks in LTE".

The next phase in the evolution of the Self-Configuring, Self-organizing and Self-optimizing network are the Self-Evolving Networks (aka. SEN) that will combine the Organizing and Optimizing features with the Self-testing and Self-Healing features. Self-testing and Self-healing have been recommended as subtasks of SON in the NGMN white paper. Self-testing and self-healing means that a system detects itself problems and mitigates or solves them avoiding user impact and significantly reducing maintenance costs.

We may still be a long way away from achieving this SEN as there are quite a few items being still standardised in 3GPP. Some of the standardised items have not yet been fully implemented and tested as well. Some of this new features that will help are listed as follows:

Automatic Radio Network Configuration Data Preparation (Rel-9)

When radio Network Elements (e.g. cells and/or eNBs) are inserted into an operational radio network, some network configuration parameters cannot be set before-hand because they have interdependencies with the configuration of operational NEs. "Dynamic Radio Network Configuration Data Preparation" comprises the generation and distribution of such interdependent parameters to the newly inserted network element and optionally already operational NEs.

This functionality allows fully automatic establishment of an eNB into a network. Otherwise an operator needs to set these configurations manually. Without this functionality self-configuration cannot be considered not fully as "self".

SON Self-healing management (Rel-10)

The target of Self-Healing (SH) is to recover from or mitigate errors in the network with a minimum of manual intervention from the operator.

Self-healing functionality will monitor and analyse relevant data like fault management data, alarms, notifications, and self-test results etc. and will automatically trigger or perform corrective actions on the affected network element(s) when necessary. This will significantly reduce manual interventions and replace them with automatically triggered re-s, re-configurations, or software reloads/upgrades thereby helping to reduce operating expense.

LTE Self Optimizing Networks (SON) enhancements (Rel-10)

This WI continues work started in Rel-9. Some cases that were considered in the initial phases of SON development are listed in the TR 36.902. From this list, almost all use cases are already specified. Capacity and Coverage Optimization (CCO) was already nominally part of the Rel-9 WI, but could not be completed due to amount of work related to other use cases. Energy Savings are a very important topic, especially for operators, as solutions derived for this use case can significantly limit their expenses. According to TR 36.902 this solution should concern switching off cells or whole base stations. This may require additional standardised methods, once there is need identified for.

Basic functionality of Mobility Load Balancing (MLB) and Mobility Robustness Optimization (MRO), also listed in TR 36.902, were defined in Rel-9. However, successful roll-out of the LTE network requires analysing possible enhancements to the Rel-9 solutions for MLB and MRO. In particular, enhancements that address inter-RAT scenarios and inter-RAT information exchange must be considered. These enhancements should be addressed in Rel-10. There may also be other use cases for LTE for which SON functionality would bring optimizations. The upcoming LTE-A brings about also new challenges that can be addressed by SON. However, since not all features are clearly defined yet, it is difficult to work on SON algorithms for them. It is therefore proposed to assign lower priority to the features specific for LTE-A.

UTRAN Self-Organizing Networks (SON) management (Rel-11)

For LTE, SON (Self-Organizing Networks) concept and many features have been discussed and standardised.

The SON target is to maintain network quality and performance with minimum manual intervention from the operator. Introducing SON functions into the UTRAN legacy is also very important for operators to minimize OPEX.

Automatic Neighbour Relation (ANR) function, specified in the LTE context, automates the discovery of neighbour relations. ANR can help the operators to avoid the burden of manual neighbour cell relations management.

Self-optimization functionalities will monitor and analyze performance measurements, notifications, and self-test results and will automatically trigger re-configuration actions on the affected network node(s) when necessary.

This will significantly reduce manual interventions and replace them with automatically triggered re-optimizations or re-configurations thereby helping to reduce operating expenses.

Minimization of Drive Tests (MDT) for E-UTRAN and UTRAN is an important topic in 3GPP Rel-10.

With the help of standardized UTRAN MDT solutions, Capacity and Coverage Optimization (CCO) for UTRAN should also be considered in UTRAN SON activities.

Study on IMS Evolution (Rel-11)

IMS network service availability largely relies on the reliability of network entity. If some critical network elements (e.g. S-CSCF, HSS) go out of service, service availability will be severely impacted. Moreover network elements are not fully utilized because network load is not usually well distributed, e.g. some nodes are often overloaded due to sudden traffic explosion, while others are under loaded to some extent. Though there’re some element level approaches to solve these problems, such as the ongoing work in CT4, the system level solution should be studied, for example, the method to distribute load between network elements in different regions especially when some disaster happens, such as earthquake.

The network expansion requires a great deal of manual configurations, and the network maintenance and upgrade are usually time-consuming and also costly for operators. Introducing self-organization features will improve the network intelligence and reduce the efforts of manual configuration. For example, upon discovering the entry point of the network, new nodes can join the network and auto-configure themselves without manual intervention. And if any node fails, other nodes will take over the traffic through the failed node timely and automatically.

The above mentioned features are just few ways in which we will achieve a truly zero-operational 4G network.

Radio-over-Fiber (RoF): The existing alternative to Femtocells

Recently while going through NTT Docomo Technical Journal, I came across an article on Radio over Fibre. This is the first time I have come across RoF but apparently this is a common way to provide indoor coverage before Femtocells.

My intention here is not to compare this with Femtocells as I can think of advantages and disadvantages of both of them.

I found the following extract in the book Femtocells: Technologies and Deployment:

Active Fibre DAS (Radio over Fibre)

Active fibre DAS is the most efficient in term of performance. Optical fibres are used to make the link between the MU and the RU. They can cover very long distances (up to 6 km) and support multiple radio services. With such a system the RU directly converts the optical signal into radio signal and vice versa. The other advantage is that optical fibre is very cheap and easy to install. Radio over fibre is now the most common technique used for indoor radio coverage. As detailed in [16], radio over fibre is today the optimal solution to extending indoor coverage, because it provides scalability, flexibility, easy expandability, and also because the signal degradation is very low compared with DAS using standard connections.

The following is from Wikipedia:

Radio over Fiber (RoF) refers to a technology whereby light is modulated by a radio signal and transmitted over an optical fiber link to facilitate wireless access. Although radio transmission over fiber is used for multiple purposes, such as in cable television (CATV) networks and in satellite base stations, the term RoF is usually applied when this is done for wireless access.

In RoF systems, wireless signals are transported in optical form between a central station and a set of base stations before being radiated through the air. Each base station is adapted to communicate over a radio link with at least one user's mobile station located within the radio range of said base station.

RoF transmission systems are usually classified into two main categories (RF-over-Fiber ; IF-over-Fiber) depending on the frequency range of the radio signal to be transported.

a) In RF-over-Fiber architecture, a data-carrying RF (Radio Frequency) signal with a high frequency (usually greater than 10 GHz) is imposed on a lightwave signal before being transported over the optical link. Therefore, wireless signals are optically distributed to base stations directly at high frequencies and converted to from optical to electrical domain at the base stations before being amplified and radiated by an antenna. As a result, no frequency up/down conversion is required at the various base station, thereby resulting in simple and rather cost-effective implementation is enabled at the base stations.

b) In IF-over-Fiber architecture, an IF (Intermediate Frequency) radio signal with a lower frequency (less than 10 GHz) is used for modulating light before being transported over the optical link. Therefore, wireless signals are transported at intermediate frequency over the optical.

Access to dead zones

An important application of RoF is its use to provide wireless coverage in the area where wireless backhaul link is not possible. These zones can be areas inside a structure such as a tunnel, areas behind buildings, Mountainous places or secluded areas such a jungle.

FTTA (Fiber to the Antenna)

By using an optical connection directly to the antenna, the equipment vendor can gain several advantages like low line losses, immunity to lightening strikes/electric discharges and reduced complexity of base station by attaching light weight Optical-to-Electrical (O/E) converter directly to antenna.