Why WCDMA peak rate is only 7.2M for China Unicom ?

伊落丹 — Thu, 08 Jul 2010 23:21:00 GMT

For HSDPA in WCDMA/UMTs, UE will be assigned a number of SF16 channelization codes by the base station during fast scheduling. Assuming a theoretical effective code rate of 1.0 and 16QAM modulation, the data rate achieved by each SF16 channelization code is given by Chip rate / SF * (bits per modulation symbol) * (code rate) = 3.84M / 16 * 4 * 1.0 = 0.96 Mb/s. while the peak data rate is 0.96 * N Mb/s, where N is the number of assigned SF16 code blocks. If the UE is assigned 15 codes, which is the maximum possible number of codes since the 1 remaining SF16 or 16*SF256 channelization code resource has to be reserved for HS-SCCH, associated DPCH and downlink common control channels, the peak rate is 0.96*15=14.4 Mb/s.

So, why is the peak rate only 7.2 Mb/s for a UE, as alleged in commercials presented by China Unicom, the only WCDMA carrier in the Heaven Kingdom? The answer lies in the HS-DSCH physical layer category. Only UEs with a capability to use up to 15 codes, such as Category 9 or 10 UEs, can reach the maximum data rate of 14.4Mb/s. Best UEs available on the market are usually Category-8 UEs that can only use up to 10 codes, resulting in a peak rate of 0.96*10=9.6 Mb/s. So why is it 7.2Mb/s? By consulting 3GPP specification 25.306 (Table 5.1a), you'll find that for a UE that can use up to 10 codes, the possible HS-DSCH transport block is 14,411 bits. For a TTI of 2ms, the peak rate is 14411bits/2ms ~= 7.2 Mb/s, whose corresponding physical layer data rate is 9.6Mb/s, where the 2.4 Mb/s in difference is consumed by channel coding and other physical layer overhead.

Now we have found the answer. The 7.2Mb/s peak rate alleged by China Unicom is actually the MAC-hs throughput for Category-8 terminals.

伊落丹 2010-07-09 07:21 发表评论

UMTS概述

伊落丹 — Wed, 15 Apr 2009 02:03:00 GMT

UMTS (Universal Mobile Telecommuniations System)

<伊落丹> illidan.modeler [at] gmail.com
Northern Capital, Republic of Pandaren

System Architecture

UTRAN

UTRAN, short for UMTS Terrestrial Radio Access Network, is a collective term for the Node B's and Radio Network Controllers which make up the UMTS radio access network.

The UTRAN allows connectivity between the UE (user equipment) and the core network. The UTRAN contains the base stations, which are called Node Bs, and Radio Network Controllers (RNC). The RNC provides control functionalities for one or more Node Bs. A Node B and an RNC can be the same device, although typical implementations have a separate RNC located in a central office serving multiple Node Bs.

The RNC and its corresponding Node Bs are called the Radio Network Subsystem (RNS). There can be more than one RNS present in an UTRAN.

Radio Resource Control

RRC handles the control plane signalling of Layer 3 between the UEs and UTRAN.

The major part of the control signalling between UE and UTRAN is RRC messages. RRC messages carry all parameters required to set up, modify and release layer 2 and layer 1 protocol entities. RRC messages also carry in their payload all higher layer signalling (mobility management (MM), connection management (CM), session management (SM), etc.). The mobility of user equipment in the connected mode is controlled by RRC signalling (measurements, handovers, cell updates, etc.).

Literature

1. [web] "UMTS Terrestrial Radio Access Network." Wikipedia, The Free Encyclopedia. 20 Apr 2009, 09:51 UTC. 21 Apr 2009 <http://en.wikipedia.org/w/index.php?title=UMTS_Terrestrial_Radio_Access_Network&oldid=284982903>.
2. [book] [Holma 2007] Section 7.8 "The Radio Resource Control Protocol"
3. [web] "Radio Resource Control." Wikipedia, The Free Encyclopedia. 12 Feb 2009, 04:30 UTC. 5 May 2009 <http://en.wikipedia.org/w/index.php?title=Radio_Resource_Control&oldid=270157640>.

伊落丹 2009-04-15 10:03 发表评论

BlogJava-伊落丹矩阵_Radio-随笔分类-UMTS

Why WCDMA peak rate is only 7.2M for China Unicom ?

UMTS概述

System Architecture

UTRAN

Radio Resource Control