Multipoint HSDPA / HSPA

The following is from 3GPP TR 25.872 - Technical Specification Group Radio Access Network; HSDPA Multipoint Transmission:

HSPA based mobile internet offerings are becoming very popular and data usage is increasing rapidly. Consequently, HSPA has begun to be deployed on more than one transmit antenna or more than one carrier. As an example, the single cell downlink MIMO (MIMO-Physical layer) feature was introduced in Release 7. This feature allowed a NodeB to transmit two transport blocks to a single UE from the same cell on a pair of transmit antennas thus improving data rates at high geometries and providing a beamforming advantage to the UE in low geometry conditions. Subsequently, in Release-8 and Release-9, the dual cell HSDPA (DC-HSDPA) and dual band DC-HSDPA features were introduced. Both these features allow the NodeB to serve one or more users by simultaneous operation of HSDPA on two different carrier frequencies in two geographically overlapping cells, thus improving the user experience across the entire cell coverage area. In Release 10 these concepts were extended so that simultaneous transmissions to a single UE could occur from four cells (4C-HSDPA).

When a UE falls into the softer or soft handover coverage region of two cells on the same carrier frequency, it would be beneficial for the non-serving cell to be able to schedule packets to this UE and thereby improving this particular user’s experience, especially when the non-serving cell is partially loaded. MultiPoint HSDPA allows two cells to transmit packets to the same UE, providing improved user experience and system load balancing. MultiPoint HSDPA can operate on one or two frequencies.

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There is also an interesting Qualcomm Whitepaper on related topic that is available to view and download here. The following is from that whitepaper:

The simplest form of Multipoint HSPA, Single Frequency Dual Cell HSPA (SFDC-HSPA), can be seen as an extension to the existing DC-HSPA feature. While DC-HSPA allows scheduling of two independent transport blocks to the mobile device (UE) from one sector on two frequency carriers, SFDC-HSPA allows scheduling of two independent transport blocks to the UE from two different sectors on the same carrier. In other words, it allows for a primary and a secondary serving cell to simultaneously send different data to the UE. Therefore, the major difference between SFDC-HSPA and DC-HSPA operation is that the secondary transport block is scheduled to the UE from a different sector on the same frequency as the primary transport block. The UE also needs to have receive diversity (type 3i) to suppress interference from the other cell as it will receive data on the same frequecny from multiple serving cells.Figure 1 llustrates the high-level concept of SFDC-HSPA.

In the case where the two sectors involved in Multipoint HSPA transmission belong to the same NodeB (Intra-NodeB mode), as illustrated in Figure 2, there is only one transmission queue maintained at the NodeB and the RNC. The queue management and RLC layer operation is essentially the same as for DC-HSPA.

In the case where the two sectors belong to different NodeBs (Inter-NodeB mode), as illustrated in Figure 2, there is a separate transmission queue at each NodeB. RLC layer enhancements are needed at the RNC along with enhanced flow control on the Iub interface between RNC and NodeB in order to support Multipoint HSPA operation across NodeBs. These enhancements are discussed in more detail in Section 4. In both modes, combined feedback information (CQI and HARQ-ACK/ NAK) needs to be sent on the uplink for both data streams received from the serving cells. On the uplink, the UE sends CQIs seen on all sectors using the legacy channel structure, with timing aligned to the primary serving cell.

When two carriers are available in the network, there is an additional degree of freedom in the frequency domain. Dual Frequency Dual Cell HSPA (DFDC-HSPA) allows exploiting both frequency and spatial domains by scheduling two independent transport blocks to the UE from two different sectors on two different frequency carriers. For a DC-HSPA capable UE, this is equivalent to having independent serving cells on the two frequency carriers. In Figure 3, UE1 is in DC-HSPA mode, whereas UE2 is in DFDC-HSPA mode.

Dual Frequency Four-Cell HSPA (DF4C-HSPA) can be seen as a natural extension of DFDC-HSPA, suitable for networks with UEs having four receiver chains. DF4C-HSPA allows use of the four receiver chains by scheduling four independent transport blocks to the UE from two different sectors on two different frequency carriers. DF4C-HSPA is illustrated in Figure 4.

Like SFDC-HSPA; DFDC-HSPA and DF4C-HSPA can also be intra-NodeB or inter-NodeB, resulting in an impact on transmission queue management, Iub flow control and the RLC layer.

Advantages of Multipoint transmission:

* Cell Edge Performance Improvement

* Load balancing across sectors and frequency carriers

* Leveraging RRU and distributed NodeB technology

Multipoint HSPA improves the performance of cell edge users and helps balance the load disparity across neighboring cells. It leverages advanced receiver technology already available in mobile devices compatible with Release 8 and beyond to achieve this. The system impact of Multipoint HSPA on the network side is primarily limited to software upgrades affecting the upper layers (RLC and RRC).

See also: FS_HSDPA_MP_TX: Study on HSDPA Multipoint Transmission

Device to Device communication (FlashLinQ?)

Recently I read on twitter that Qualcomm has asked 3GPP to do a study on device to device communication. Sometime back I blogged about FlashLinQ, Qualcomm's proprietary P2P communication technology. I am not sure if Qualcomm is pushing for this one or wants to have a study in general. If you know more details please add as comments.

Meanwhile, I found this video that explains what FlashLinQ does:

And there is also this presentation which is less technical and explains the information in the video.

FlashlinQ – Direct Device-to-Device Communication Technology

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More technically detailed presentation embedded in my earlier blog post here.

Ultra Self Organising Networks (UltraSON)

While watching the Femtocell Video, I was a bit curious on what exactly UltraSON does, so I decided trying to find more info. Surprisingly the information was hard to come by. I finally managed to find the Qualcomm site that has more details but surprisingly it wasnt east to find. From the website (link at bottom):

Qualcomm femtocell R&D program is focused on developing self organizing network features to address interference and mobility management for femtocell deployment in residential and enterprise environments. Interference and mobility management is a chief concern especially when operators are planning for high levels of perfromace from dense and an unplanned femtocell deployments. Qualcomm has developed UltraSON™, a comprehensive suite of interference and mobility management techniques for femtocell deployments in residential and enterprises.

The techniques that make UltraSON:

More details on UltraSON at : http://www.qualcomm.com/research/femtocells

Interesting promotional Femtocell video by Qualcomm

2020: Radio and Mobile Broadband (MBB) Beyond 4G

An interesting presentation and whitepaper from Nokia Siemens Networks embedded below:

Mobile Broadband Beyond 4G

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Nokia siemens networks beyond 4 g white paper online 20082011

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Related post: 2020: More than 50 Billion connected devices - Ericsson

Two interesting NGMN papers on Backhaul

There are some interesting blog posts on Broadband Traffic Managemenet on Backhaul. Here are few excerpts:

Traditional network management practice says that network element usage level should not exceed 70% of its capacity. If it does - it is time to do something - buy more or manage it better. So, according to a recent Credit Suisse report - it is time to do something for wireless networks, globally. For North America, where current utilization at peak time reaches 80% it is even urgent.

Phil Goldstein (pictured) reports to FierceWireless that - "Wireless networks in the United States are operating at 80 percent of total capacity, the highest of any region in the world, according to a report prepared by investment bank Credit Suisse. The firm argued that wireless carriers likely will need to increase their spending on infrastructure to meet users' growing demands for mobile data .. globally, average peak network utilization rates are at 65 percent, and that peak network utilization levels will reach 70 percent within the next year. .. 23 percent of base stations globally have capacity constraints, or utilization rates of more than 80 to 85 percent in busy hours, up from 20 percent last year .. In the United States, the percentage of base stations with capacity constraints is 38 percent, up from 26 percent in 2010"

And

The Yankee Group provides the following forecast for mobile backhaul:

Average macrocell backhaul requirements were 10 Mbps in 2008 (seven T1s, five E1s). In less than three years, they have more than tripled to 35 Mbps in 2011, and by 2015, Yankee Group predicts they will demand 100 Mbps.

There were 2.4 million macro cell site backhaul connections worldwide in 2010, growing to 3.3 million by [2015?]

Yankee's new research conclude:

"The market for wholesale backhaul services in North America will grow from $2.45 billion in 2010 to $3.9 billion in 2015, with the majority of this growth coming from Ethernet backhaul. Successful backhaul service providers will be those that can demonstrate price/performance and reliability, have software tools in place and can meet the specific needs of the mobile market.

And recently:

A Dell'Oro Group report forecasts that "Mobile Backhaul market revenues are expected to approach $9B by 2015. This updated report tracks two key market segments: Transport, which includes microwave and optical equipment, and Routers and Switches, which includes cell site devices, carrier Ethernet switches, and service provider edge routers .. routers and switches expected to constitute 30% of mobile backhaul market "

Shin Umeda, Vice President of Routers research at Dell’Oro Group said: “Our research has found that operators around the world are concerned with the rate of mobile traffic growth and are transitioning to Internet Protocol (IP) technologies to build a more efficient and scalable backhaul network. Our latest report forecasts the demand for IP-based routers and switches will continue to grow through 2015, almost doubling the market size of the Router and Switches segment in the five-year forecast period”

I have some basic posts on why Backhaul is important, here and here.

NGMN has timely released couple of whitepapers on the Backhaul.

The first one, 'Guidelines for LTE Backhaul Traffic Estimation' document describes how a model is developed to predict traffic levels in transport networks used to backhaul LTE eNodeBs. Backhaul traffic is made up of a number of different components of which user plane data is the largest, comprising around 80-90% of overall traffic, slightly less when IPsec encryption is added. These results reveal that the cell throughput characteristics for data carrying networks are quite different to those of voice carrying networks.

The purpose of second one, 'NGMN Whitepaper LTE Backhauling Deployment Scenarios' is to support operators in their migration from current architectures to new, packet-based backhaul networks. With the introduction of LTE operators need to look at how the backhauling network, the network domain that connects evolved NodeBs (eNBs) to MME and S/P-GW, is capable of adapting to the new requirements, namely the adoption of a packet infrastructure, without disrupting the existing services. This paper introduces some reference architectures, moving from a pure layer 2 topology to a full layer 3 one, discussing some elements to be considered in the design process of a network.

They are both long but interesting read if you like to learn more about Backhaul and the best way in future proofing the network deployments.

LTE Advanced HetNet Benefits!

Presentation from Qualcomm Webinar, LTE-Advanced Hetnet benefits.

LTE Advanced HetNet Benefits!

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Qualcomm is undisputed leader in the LTE chipsets and have been pushing hard for the next generation LTE-A chipsets. Here is a promotional LTE-Advanced Video on Youtube:

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.

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

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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