Our World Without Mobile :-)

Decision Tree of Transmission Modes (TM) for LTE

4G Americas have recently published whitepaper titled "MIMO and Smart Antennas for Mobile Broadband Systems" (available here). The above picture and the following is from that whitepaper:

Figure 3 above shows the taxonomy of antenna configurations supported in Release-10 of the LTE standard (as described in 3GPP Technical Specification TS 36.211, 36.300). The LTE standard supports 1, 2, 4 or 8 base station transmit antennas and 2, 4 or 8 receive antennas in the User Equipment (UE), designated as: 1x2, 1x4, 1x8, 2x2, 2x4, 2x8, 4x2, 4x4, 4x8, and 8x2, 8x4, and 8x8 MIMO, where the first digit is the number of antennas per sector in the transmitter and the second number is the number of antennas in the receiver. The cases where the base station transmits from a single antenna or a single dedicated beam are shown in the left of the figure. The most commonly used MIMO Transmission Mode (TM4) is in the lower right corner, Closed Loop Spatial Multiplexing (CLSM), when multiple streams can be transmitted in a channel with rank 2 or more.

Beyond the single antenna or beamforming array cases diagrammed above, the LTE standard supports Multiple Input Multiple Output (MIMO) antenna configurations as shown on the right of Figure 3. This includes Single User (SU-MIMO) protocols using either open loop or closed loop modes as well as transmit diversity and Multi-User MIMO (MU-MIMO). In the closed loop MIMO mode, the terminals provide channel feedback to the eNodeB with Channel Quality Information (CQI), Rank Indications (RI) and Precoder Matrix Indications (PMI). These mechanisms enable channel state information at the transmitter which improves the peak data rates, and is the most commonly used scheme in current deployments. However, this scheme provides the best performance only when the channel information is accurate and when there is a rich multi-path environment. Thus, closed loop MIMO is most appropriate in low mobility environments such as with fixed terminals or at pedestrian speeds.

In the case of high vehicular speeds, Open Loop MIMO may be used, but because the channel state information is not timely, the PMI is not considered reliable and is typically not used. In TDD networks, the channel is reciprocal and thus the DL channel can be more accurately known based on the uplink transmissions from the terminal (the forward link’s multipath channel signature is the same as the reverse link’s – both paths use the same frequency block). Thus, MIMO improves TDD networks under wider channel conditions than in FDD networks.

One may visualize spatial multiplexing MIMO operation as subtracting the strongest received stream from the total received signal so that the next strongest signal can be decoded and then the next strongest, somewhat like a multi-user detection scheme. However, to solve these simultaneous equations for multiple unknowns, the MIMO algorithms must have relatively large Signal to Interference plus Noise ratios (SINR), say 15 dB or better. With many users active in a base station’s coverage area, and multiple base stations contributing interference to adjacent cells, the SINR is often in the realm of a few dB. This is particularly true for frequency reuse 1 systems, where only users very close to the cell site experience SINRs high enough to benefit from spatial multiplexing SU-MIMO. Consequently, SU-MIMO works to serve the single user (or few users) very well, and is primarily used to increase the peak data rates rather than the median data rate in a network operating at full capacity.

Angle of Arrival (AoA) beamforming schemes form beams which work well when the base station is clearly above the clutter and when the angular spread of the arrival is small, corresponding to users that are well localized in the field of view of the sector; in rural areas, for example. To form a beam, one uses co-polarized antenna elements spaced rather closely together, typically lamda/2, while the spatial diversity required of MIMO requires either cross-polarized antenna columns or columns that are relatively far apart. Path diversity will couple more when the antennas columns are farther apart, often about 10 wavelengths (1.5m or 5’ at 2 GHz). That is why most 2G and 3G tower sites have two receive antennas located at far ends of the sector’s platform, as seen in the photo to the right. The signals to be transmitted are multiplied by complex-valued precoding weights from standardized codebooks to form the antenna patterns with their beam-like main lobes and their nulls that can be directed toward sources of interference. The beamforming can be created, for example, by the UE PMI feedback pointing out the preferred precoder (fixed beam) to use when operating in the closed loop MIMO mode TM4.

For more details, see the whitepaper available here.

Related posts:

• LTE-A: Downlink Transmission Mode 9 (TM-9)
• R&S Whitepaper: LTE Transmission Modes and Beamforming

What's next with 802.11!

From another brilliant presentation by R&S from their LTE Summit 2013. Last year I had a similar overview from Agilent here. This one is much more detailed on what's coming next for WiFi.

802.11: a jet plane window’s view from Zahid Ghadialy

Introduction to M2M and its developments in LTE

LTE Innovation Summit 2013 - Anandamoy Sen from Rohde & Schwarz on Vimeo.

An interesting video on Introduction to M2M and its developments in LTE from Rohde&Schwarz LTE Innovation Summit 2013.

The presentation is also embedded below and can be downloaded from Slideshare.

Introduction to M2M by Sierra Wireless from Zahid Ghadialy

Present and Future Technologies for Internet of Things (IoT)

An Interesting presentation from our Future of Wireless Conference (#FWIC2013) in Cambridge earlier this month. A question being asked is what technology will be used for Internet of Things (IoT) or Internet of Everything (IoE) as its also referred to nowadays. These 3 slides below summarises what technologies are see applicable to which scenarios.

Complete slides are embedded below and if you like to see the video, its available here.

Mapping the Future of the Internet of (Every)Thing(s) from Zahid Ghadialy

Small Cells Enhancements for 3GPP Release-12

The following presentation is by 3GPP in the not so long ago, Small Cells World Summit 2013.

Enhancements for Small Cells in 3GPP Release-12 from Zahid Ghadialy

Related Post:

• Small cell standardization in 3GPP Release 12

Adaptive Video Streaming: Principles, Improvements and Innovation

An Interdigital presentation from last year explains the principle of adaptive streaming very well for those who would not know how it worked.

This process of adaptation could be improved based on the quality of coverage at any particular time.

Interdigital are proposing a further enhancement of improving the adaptation further based on the User behaviour. If for example the user is far away then the quality need not be great on the device. On the other hand if the user is very close-by, the quality should be as good as it can get. They have explained it in a whitepaper for whoever is interested here.

A video showing this method is embedded below:

500 Billion devices by 2030, etc...

Few weeks back in the LTE World Summit 2013, I heard someone from Ericsson mention that internally they think that by 2030 there will be 500 Billion Connected devices on the planet. The population projections for 2030 is somewhere around 8.5 Billion people worldwide. As a result the figure does not come much as a surprise to me.

John Cunliffe from Ericsson is widely credited for making the statement 50 Billion connected devices by 2020. Recently he spoke in the Cambridge Wireless and defended his forecast on the connected devices. He also provided us with the traffic exploration tool to see how the devices market would look up till 2018. Here is one of the pictures using the tool:

In terms of Cellular connectivity, we are looking at 9 Billion devices by 2018. The interesting thing to notice is that in 2017, there are still some 4 Billion feature phones. While in the developed world our focus is completely on Smartphones, its interesting to see new and existing SMS/USSD based services are still popular in the developing world. Some months back I heard about Facebook developing SMS/USSD based experience for Feature phones, I am sure that would attract a lot of users from the developing world.

One thing missing from the above is non-cellular connections which will make bulk of connectivity. Wi-Fi for example is a major connectivity medium for tablets. In fact 90% of the tablets have only WiFi connectivity. Bluetooth is another popular method of connectivity. While its mostly used in conjunction with phones, it is going to be a popular way of connecting devices in the Personal Area Network's (PAN's). So its no surprise that we will see 50 Billion connected devices but maybe not by 2020. My guess would be around 2022-23.

Is it too early to talk '5G'

While LTE/LTE-A (or 4G) is being rolled out, there is already a talk about 5G. Last week in the LTE World Summit in Amsterdam, there was a whole track on what should 5G be without much technical details. Couple of months back Samsung had announced that they have reached 5G breakthrough. In my talk back in May, I had suggested that 5G would be an evolution on the Radio Access but the core will evolve just little. Anyway, its too early to speculate what the access technology for 5G would be.

Ericsson has published a '5G' whitepaper where they talk about the vision and why and what of 5G rather than going into any technical details. It is embedded below:

5G: What is it? from Ericsson

Multi-RAT mobile backhaul for Het-Nets

Recently got another opportunity to hear from Andy Sutton, Principal Network Architect, Network Strategy, EE. His earlier presentation from our Cambridge Wireless event is here. There were many interesting bits in this presentation and some of the ones I found interesting is as follows:

Interesting to see in the above that the LTE traffic in the backhaul is separated by the QCI (QoS Class Identifiers - see here) as opposed to the 2G/3G traffic.

This is EE's implementation. As you may notice 2G and 4G use SRAN (Single RAN) while 3G is separate. As I mentioned a few times, I think 3G networks will probably be switched off before the 2G networks, mainly because there are a lot more 2G M2M devices that requires little data to be sent and not consume lots of energy (which is an issue in 3G), so this architecture may be suited well.

Finally, a practical network implementation which looks different from the text book picture and the often touted 'flat' architecture. Andy did mention that they see a ping latency of 30-50ms in the LTE network as opposed to around 100ms in the UMTS networks.

Mark Gilmour was able to prove this point practically.

Here is the complete presentation: