TD-LTE again in Focus

TD-LTE has been in news since some time and is making WiMAX proponents nervous. Here is quick summary of what has happend in last couple of weeks.

MediaTek Inc and Qualcomm are seeking the opportunity brought by the construction of TD-LTE network by China Mobile. China Mobile is seeking to test its TD-LTE networks in three coastal cities first, namely Qingdao, Xiamen, and Zhuhai, in the second half of 2010. Qualcomm is also bidding for TD-LTE spectrum in India.

Earlier this week, Japanese cellco Softbank Mobile said that it is considering deploying the Chinese-developed TD-LTE standard as a 4G network. Senior executive vice president Ted Matsumoto told telecomasia.net the company could deploy it in the 2.5GHz spectrum it gained access to when it bought a stake in failing PHS operator Willcom last month.

“We’re going to have 2.5GHz TDD spectrum, so we will seriously explore TD-LTE,” he said. Softbank is also focused on winning access to the key 700MHz or 900MHz frequencies, the “golden spectrum” with a much higher propagation range already that is used by both of its competitors.

According to FierceBroadbandWireless, Ericsson has already signed an MoU to create a strategic cooperation with Datang Telecom in China to develop TDD solutions and likely gain a foothold in China Mobile's planned TD-LTE network.

Motorola, the only vendor to heavily tout LTE in TDD spectrum, is heavily leveraging its expertise in WiMAX, which operates in the TDD band, to do so. It has been targeting China Mobile for some time and is demonstrating TD-LTE capabilities in China Mobile's showcase TD-LTE network in Shanghai. It is aggressively gearing up for the World Expo 2010 in Shanghai, China, to showcase its momentum in TD-LTE.

Nokia Siemens Networks is not behind and has opened a TD-LTE lab aimed at accelerating commercial TD-LTE device deployments.

Some informative links are below for further reading

MediaTek, Qualcomm Eyeing TD-LTE Chip Market

700MHz band for LTE in Taiwan

Softbank Mobile mulls TD-LTE for 2.5GHz

Motorola's TD-LTE Expertise

See my an old blog to know more about TD-LTE What is TD-LTE and Why the sudden interest in TD-LTE

source:LteWorld Blog

WiMAX or LTE : which one is better?

WiMAX or LTE – which is better? Answer depends on who you talk to. The vendors have their own views, and the operators theirs. Consumers does not think about technology. It is about speed and seamless connectivity, and not having to buy different devices to operate on different platforms.

WiMAX is being deployed at a steady pace worldwide and will try to grab major customers in the market. Operators world wide are doing LTE trials and in Europe Telesonera also has lauched LTE services last year in December. In North america Verizon is set to launch LTE services in Q4, 2010.

Both WiMAX and LTE are based on IP packet-based data carriage, in contrast to 3G and earlier cellphone systems which were designed to accommodate circuit-switched communication. The LTE specification comes from a background of cellular telephony. It would not be surprising if LTE's QoS arrangement and more elaborate upstream and downstream arrangements make it more suitable for voice.

When used primarily for a handheld device with cellphone functions, LTE is at a considerable advantage in that when the device is beyond range of LTE base stations, it can fall back to 2.5G and 3G services, assuming it has the requisite radio technologies, with potentially seamless handover.

For operators, the choice of technology depends on a number of things including available spectrum, legacy inter-working, timing and business focus. To deploy either technology, operators will have to commit tens of billions of dollars in network upgrades for the new mobility landscape, which now includes social, video, location-based and entertainment applications and experiences.

In many countries, the current generation of mobile telecoms networks is 2.5G or 3G. In India, as the 3G auction is underway, the successful foray of WiMAX (a BWA technology) is not only being threatened by another BWA technology called Long Term Evolution Time Division Duplex or TD-LTE.

So which technology has the advantageous position? This is where the debate lies. While LTE invokes the impression of mobility, seamless connectivity (due to 2G, 3G fallback), WiMax invokes the impression of computing. So in the end its all about consumers and How they would like to use them.

Recent introduction of Overdirive by Sprint has again given another dimension to mobile WiFi Hot Spots, LTE may follow same route as well.

Found an interesting presentation on LTE Vs WiMAX, by Mario Eguiluz Alebicto, sharing with you all.

Analysis WiMax vs LTE

View more presentations from Mario Eguiluz Alebicto.

source: LteWorld Blog by Jai

Sprint shows the way for LTE/3G Overdrive

Sprint recently lauched a 3G/4G router named as Overdrive. It’s a WiMAX modem that connects to 4G broadband wherever the service is offered. Overdrive also has a fail safe mechanism to connect to a 3G network when the device isn’t in a WiMAX market.

Similar device would be suitable for LTE market as well. I haven't come across any such device supporting LTE/3G and acting as WiFi modem. Brining Overdrive like device to LTE will boost LTE growth and would offer subscribers uninterupted service in initial deployments. I would prefer support of HSPA+ as well in such a device.

Sprint also has also started offering an interesting bundle package in their accessories store. The 4G Case is designed to hold iPad, plus the the Overdrive.

With the Sprint Overdrive(TM) 3G/4G Mobile Hotspot, you can surf the web on your device up to 10 times faster than 3G. Sprint 4G covers 28 major markets such as Atlanta, Baltimore, Chicago, Dallas/Ft. Worth, Las Vegas, Philadelphia, Portland, Ore., San Antonio and Seattle. In 2010, Sprint will launch many more markets, and is expected to cover up to 120 million people with Sprint 4G service.

source: Lteworld

Automatic Neighbour Relation in LTE

Manually provisioning and managing neighbor cells in traditional mobile network is challenging task and it becomes more difficult as new mobile technologies are being rolled out while 2G/3G cells already exist. For LTE, task becomes challenging for operators, as in addition of defining intra LTE neighbour relations for eNBs operator has to provision neighboring 2G, 3G, CDMA2000 cells as well.

According to 3GPP specifications, the purpose of the Automatic Neighbour Relation (ANR) functionality is to relieve the operator from the burden of manually managing Neighbor Relations (NRs). This feature would operators effort to provision

Figure below shows ANR and its environment as per 3GPP. It shows interaction between eNB and O&M due to ANR.

The ANR function resides in the eNB and manages the conceptual Neighbour Relation Table (NRT). Located within ANR, the Neighbour Detection Function finds new neighbours and adds them to the NRT. ANR also contains the Neighbour Removal Function which removes outdated NRs. The Neighbour Detection Function and the Neighbour Removal Function are implementation specific.

An existing Neighbour cell Relation (NR) from a source cell to a target cell means that eNB controlling the source cell knows the ECGI/CGI and Physical Cell Identifier (PCI) of the target cell and has an entry in the NRT for the source cell identifying the target cell.

For each cell that the eNB has, the eNB keeps a NRT. For each NR, the NRT contains the Target Cell Identifier (TCI), which identifies the target cell. For E-UTRAN, the TCI corresponds to the E-UTAN Cell Global Identifier (ECGI) and Physical Cell Identifier (PCI) of the target cell.

The ANR function relies on cells broadcasting their identity on global level, E-UTRAN Cell Global Identifier (ECGI) and allows O&M to manage the NRT. O&M can add and delete NRs. It can also change the attributes of the NRT. The O&M system is informed about changes in the NRT.

Intra-LTE/frequency ANR:

The eNB serving cell with ANR function, instructs each UE to perform measurements on neighbor cells, as a part of the normal call procedure. The eNB may use different policies for instructing the UE to do measurements, and when to report them to the eNB.

When UE discovers new cell’s ECGI, the UE reports the detected ECGI to the serving cell eNB. In addition the UE reports the tracking area code and all PLMN IDs that have been detected. The eNB adds this neighbour relation to NRT.

Inter-RAT/Inter-frequency ANR:

The eNB serving cell with ANR function can instruct a UE to perform measurements and detect cells on other RATs/frequencies .during connected mode. The eNB may use different policies for instructing the UE to do measurements, and when to report them to the eNB.

The UE reports the PCI of the detected cells in the target RATs/frequencies. When the eNB receives UE reports containing PCIs of cell(s), eNB may instruct the UE to read the CGI and the RAC of the detected neighbour cell in case of GERAN detected cells and CGI, LAC and, RAC in case of UTRAN detected cells. For the Interfrequency case, the eNB may instruct the UE to read the ECGI, TAC and all available PLMN ID(s) of the inter-frequency detected cell.

The eNB updates its inter-RAT/inter-frequency Neighbour Relation Table after receiving relevant info from UE.

India 3G Spectrum Bids Reach $1.3 Billion

Bids for an all-India license to offer 3G services reached 56.2 billion rupees ($1.3 billion) on the seventh day of auction, according to a statement on the department of telecommunications Web site. This amount is approximately 63% higher than the total Rs.35 billion, that was estimated to be gathered before the commencement of the auction.

On day seven of the 3G spectrum auction, 6 more rounds were completed making the total number of rounds to 40.

Nine mobile-phone carriers including Vodafone Group Plc, the world’s largest, and Bharti Airtel Ltd., India’s biggest, are vying for the spectrum to offer third-generation services in the world’s second-largest wireless market by subscribers.

The government is auctioning spectrum for operating 3G services in India’s 22 designated telephone zones. It plans to sell 93 licenses to provide high-speed data to mobile phones and computers that may raise an estimated 500 billion rupees, helping reduce the nation’s fiscal deficit.

source: http://lteworld.org/blog/india-3g-spectrum-bids-reach-13-billion

LTE Handovers - Intra E-UTRAN Handover

Intra E-UTRAN Handover is used to hand over a UE from a source eNodeB to a target eNodeB using X2 when the MME is unchanged. In the scenario described here Serving GW is also unchanged. The presence of IP connectivity between the Serving GW and the source eNodeB, as well as between the Serving GW and the target eNodeB is assumed.

The intra E-UTRAN HO in RRC_CONNECTED state is UE assisted NW controlled HO, with HO preparation signalling in E-UTRAN.

To prepare the HO, the source eNB passes all necessary information to the target eNB (e.g. E-RAB attributes and RRC context) and UE accesses the target cell via RACH following a contention-free procedure using a dedicated RACH preamble.

The HO procedure is performed without EPC involvement, i.e. preparation messages are directly exchanged between the eNBs. The figure below shows the basic handover scenario where neither MME nor Serving Gateway changes:

Detailed explanation of above scenario is below.

• The source eNB configures the UE measurement procedures according to the area restriction information. UE sends MEASUREMENT REPORT by the rules set by i.e. system information, specification etc.
• Source eNB makes decision based on MEASUREMENT REPORT and RRM information to hand off UE and issues a HANDOVER REQUEST message to the target eNB passing necessary information to prepare the HO at the target side.
• Admission Control may be performed by the target eNB dependent on the received E-RAB QoS information to increase the likelihood of a successful HO. The target eNB configures the required resources according to the received E-RAB QoS information.
• Target eNB prepares HO with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source eNB. The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to be sent to the UE as an RRC message to perform the handover.
• The UE receives the RRCConnectionReconfiguration message with necessary parameters (i.e. new C-RNTI, target eNB security algorithm identifiers, and optionally dedicated RACH preamble, target eNB SIBs, etc.) and is commanded by the source eNB to perform the HO.
• The source eNB sends the SN STATUS TRANSFER message to the target eNB to convey the uplink PDCP SN receiver status and the downlink PDCP SN transmitter status of E-RABs for which PDCP status preservation applies (i.e. for RLC AM).
• After receiving the RRCConnectionReconfiguration message including the mobilityControlInformation , UE performs synchronisation to target eNB and accesses the target cell via RACH.
• The target eNB responds with UL allocation and timing advance.
• UE sends the RRCConnectionReconfigurationComplete message (C-RNTI) to confirm the handover to the target eNB to indicate that the handover procedure is completed for the UE. The target eNB verifies the C-RNTI sent in the RRCConnectionReconfigurationComplete message. The target eNB can now begin sending data to the UE.
• The target eNB sends a PATH SWITCH message to MME to inform that the UE has changed cell.
• The MME sends an UPDATE USER PLANE REQUEST message to the Serving Gateway.
• The Serving Gateway switches the downlink data path to the target side. The Serving gateway sends one or more "end marker" packets on the old path to the source eNB and then can release any U-plane/TNL resources towards the source eNB.
• Serving Gateway sends an UPDATE USER PLANE RESPONSE message to MME.
• The MME confirms the PATH SWITCH message with the PATH SWITCH ACKNOWLEDGE message.
• By sending UE CONTEXT RELEASE, the target eNB informs success of HO to source eNB and triggers the release of resources by the source eNB. The target eNB sends this message after the PATH SWITCH ACKNOWLEDGE message is received from the MME.
• Upon reception of the UE CONTEXT RELEASE message, the source eNB can release radio and C-plane related resources associated to the UE context. Any ongoing data forwarding may continue.

Source : 3GPP TS 36.300

What is TD-LTE and Why the sudden interest in TD-LTE?

TDD (time division duplex) version of LTE is known as TD-LTE. Recently operators and vendors across world have requested the 3GPP standards body to begin working on specifications that would enable TD-LTE to be deployed in the 2.6 GHz band of spectrum as well. This frequency band is currently used for WiMAX and would allow operators like Clearwire to make it possible to deploy TD-LTE at 2.6GHz in the US.

A recent article from Fierce broadband wireless puts reason of renewed interest as below

• The FDD LTE and TD-LTE versions of the 3GPP standard are very similar. As a result, devices can support both the FDD and TDD interfaces through a single chipset--i.e., without any additional cost. This is a hugely important new development: TD-LTE will benefit from the wide availability of FDD LTE devices that will be able to support TD-LTE as well. Unlike WiMAX, TD-LTE does not need to prove to have a substantial market share to convince vendors to develop devices. Vendors do not need to develop new devices, they simply need to add TD-LTE support to the existing ones.
• There is a lot of TDD spectrum available, and in most cases it is cheaper and under-utilized. 3G licenses frequently have TDD allocations and upcoming 2.5 GHz auction in most cases contemplate TDD bands.
• The increasing availability of base stations that can be cost-effectively upgraded will make it possible and relatively inexpensive for WiMAX operators to transition to TD‑LTE using the same spectrum allocation. The transition will still require substantial efforts and be justified only in some cases, but it will make it easier for WiMAX operators to have roaming deals and to have access to the same devices that LTE operators have.
• Industry commitment to WiMAX 16m, the ITU-Advanced version of WiMAX and successor to the current WiMAX 16e, is still limited.

The proposal is to adopt the 2496MHz-to-2690MHz frequency band in the US for TD-LTE. Part of the 2.6GHz band is already specified for TDD, namely the 2570MHz-to-2620MHz band.

Currently, the LTE standards support both FDD and TDD operation. Fifteen paired (for FDD operation) and eight unpaired (for TDD operation) spectrum bands have already been identified by the 3GPP for LTE as shown below.

E‑UTRA Operating Band	Uplink (UL) operating band BS receive UE transmit			Downlink (DL) operating band BS transmit UE receive			Duplex Mode
	FUL_low – FUL_high			FDL_low – FDL_high
1	1920 MHz	–	1980 MHz	2110 MHz	–	2170 MHz	FDD
2	1850 MHz	–	1910 MHz	1930 MHz	–	1990 MHz	FDD
3	1710 MHz	–	1785 MHz	1805 MHz	–	1880 MHz	FDD
4	1710 MHz	–	1755 MHz	2110 MHz	–	2155 MHz	FDD
5	824 MHz	–	849 MHz	869 MHz	–	894MHz	FDD
6	830 MHz	–	840 MHz	875 MHz	–	885 MHz	FDD
7	2500 MHz	–	2570 MHz	2620 MHz	–	2690 MHz	FDD
8	880 MHz	–	915 MHz	925 MHz	–	960 MHz	FDD
9	1749.9 MHz	–	1784.9 MHz	1844.9 MHz	–	1879.9 MHz	FDD
10	1710 MHz	–	1770 MHz	2110 MHz	–	2170 MHz	FDD
11	1427.9 MHz	–	1447.9 MHz	1475.9 MHz	–	1495.9 MHz	FDD
12	698 MHz	–	716 MHz	728 MHz	–	746 MHz	FDD
13	777 MHz	–	787 MHz	746 MHz	–	756 MHz	FDD
14	788 MHz	–	798 MHz	758 MHz	–	768 MHz	FDD
…
17	704 MHz	–	716 MHz	734 MHz	–	746 MHz	FDD
...
33	1900 MHz	–	1920 MHz	1900 MHz	–	1920 MHz	TDD
34	2010 MHz	–	2025 MHz	2010 MHz	–	2025 MHz	TDD
35	1850 MHz	–	1910 MHz	1850 MHz	–	1910 MHz	TDD
36	1930 MHz	–	1990 MHz	1930 MHz	–	1990 MHz	TDD
37	1910 MHz	–	1930 MHz	1910 MHz	–	1930 MHz	TDD
38	2570 MHz	–	2620 MHz	2570 MHz	–	2620 MHz	TDD
39	1880 MHz	–	1920 MHz	1880 MHz	–	1920 MHz	TDD
40	2300 MHz	–	2400 MHz	2300 MHz	–	2400 MHz	TDD

What is difference in between LTE FDD & TDD?

In both LTE FDD and LTE TDD, the transmitted signal is organized into subframes of 1 millisecond (ms) duration and 10 subframes constitute a radio frame. Each subframe normally consists of 14 OFDM symbols (12 OFDM symbols in case of the so-called “Extended Cyclic Prefix”).

Although the frame structure is, in most respects, the same for LTE FDD and LTE TDD, there are some differences between the two, most notably the use of special subframes in TDD. Another difference is the other subframes are allocated either for uplink transmission or for downlink transmission.

In case of FDD operation, there are two carrier frequencies, one for uplink transmission (fUL) and one for downlink transmission (fDL). During each frame, there are consequently 10 uplink subframes and 10 downlink subframes and uplink and downlink transmission can occur simultaneously within a cell.

In case of TDD operation, there is only one single carrier frequency and uplink and downlink transmissions in the cell are always separated in time. As the same carrier frequency is used for uplink and downlink transmission, both the base station and the mobile terminals must switch from transmission to reception and vice versa. Thus, as a subframe is either an uplink subframe or a downlink subframe, the number of subframes per radio frame in each direction is less than 10.

Further readings: 3GPP LTE for TDD Spectrum in the Americas, 3GPP standards