Hello folks,
I am learning UMTS and LTE nowadays and thought of sharing some wireless related stuff with you guys And sorry, this is not related to any Mobile OS; instead I would be posting 3G/4G fundamentals, architecture, protocol stacks, call flows and other real life scenarios worth sharing.

To start with, I would be posting UMTS related stuff (WCDMA) and would be concentrating mostly on Layer 2 (MAC) and that too on Mac-hs (HSDPA).

And yes, you would get all the related stuff on internet, but I am planning to put everything at one place

I'd be updating this thread on a regular basis. So stay tuned if you are interested and you are most welcome to share your wireless knowledge on this thread

Thank you thedead1440 for redirecting me to this section

Reserved for Index.

UMTS architecture



Iu-CS is the interface between RNC and Circuit switched core network. See this.

UMTS Capabilities
The UMTS cellular system as defined under the 3GPP Release 99 standard was orientated more towards switched circuit operation and was not well suited to packet operation (If I am not wrong, it supported only 384 kbps data rate in the DL). Additionally greater speeds were required by users than could be provided with the original UMTS networks. Accordingly the changes required for 3G HSPA were incorporated into many UMTS networks to enable them to operate more in the manner required for current applications.

• UMTS uses Wideband CDMA (WCDMA) as the radio transmission standard.
• 5 MHz channel bandwidth.
• With HSDPA and HSUPA (3GPP release5 & 6), upto 14.4 Mbps transmission speed in the DL and 5.76 Mbps speed in the UL; with DC and MIMO, even more

The low data rates with R99 UMTS basically paved the way for the introduction of HSPA. Some architectural changes were done on the network elements and the Node B (BTS) became a bit more intelligent and more functional. Many of the RNC functions has now been moved to Node B as well as introduction of Mac-hs and Mac-e in the UE and in the Node B.

With HSPA, these are the notable improvements.

• Use of higher order modulation: Instead of QPSK, now we use 16 QAM as well.
• Shorter Transmission Time Interval (TTI): HSDPA now use 2 ms TTI.
• Use of shared channel transmission: HS-PDSCH (will be discussed later).
• Use of link adaptation: Based on the dynamic channel conditions.
• Fast Node B scheduling: Every 2 ms.
• Node B based Hybrid ARQ: HARQ: Erroneous packets are combined with the newly received packet to decode the original packet

Unfortunately this is way off-topic. In particular:
this advice was wrong. The brainstorm category is (now obsolete) for discussing new features to be implemented on Maemo. Looking at talk.maemo.org front page you see that the brainstorm forum is about:

"Constructive discussion about proposals filed at http://maemo.org/community/brainstorm/"

See also http://talk.maemo.org/showpost.php?p=353146&postcount=1

"Threads here MUST HAVE a related Brainstorm proposal linked. You have the rest of Talk to have free-form discussion."

But hey, do as you like.

Forgot to mention the various 3GPP releases. Here it is (starting from Rel. 5)

• Release 4: This release of the 3GPP standard provided for the efficient use of IP, a facility that was required because the original Release 99 focussed on circuit switched technology. Accordingly this was a key enabler for 3G HSDPA.
• Release 5: This release included the core of HSDPA itself. It provided for downlink packet support, reduced delays, a raw data rate (i.e. including payload, protocols, error correction, etc) of 14 Mbps and gave an overall increase of around three over the 3GPP UMTS Release 99 standard.
• Release 6: This included the core of HSUPA with an enhanced uplink with improved packet data support. This provided reduced delays, an uplink raw data rate of 5.74 Mbps
• Release 7: This release of the 3GPP standard included downlink MIMO operation as well as support for higher order modulation up to 64 QAM in the uplink and 16 QAM in the downlink. However it only allows for either MIMO or the higher order modulation. It also introduced protocol enhancements to allow the support for Continuous Packet Connectivity (CPC).
• Release 8: First LTE release. This release of the standard defines dual carrier operation as well as allowing simultaneous operation of the high order modulation schemes and MIMO. Further to this, latency is improved to keep it in line with the requirements for many new applications being used.
• Release 9: SAES Enhancements, WiMAX and LTE/UMTS Interoperability. Dual-Cell HSDPA with MIMO, Dual-Cell HSUPA.
• Release 10: LTE Advanced fulfilling IMT Advanced 4G requirements. Backwards compatible with release 8 (LTE). Multi-Cell HSDPA (4 carriers).
• Release 11: Advanced IP Interconnection of Services. Service layer interconnection between national operators/carriers as well as third party application providers.

I was not aware. Sorry - I've requested to move this thread to off-topic

I don't really know the forum rules and policies and never did go through them. The reason is I rarely post in sections other than off-topic, and that too I restrict myself to Dave's countdown thread thedead1440 suggested me to open the thread either in General or in Brainstorm. I myself decided to put it here. My bad

And yeah, once again, if I am not supposed to post things which are not related to Maemo/MeeGo, I can stop it right away

Thread on hold

EDIT: Since the thread has been moved to off-topic, let me continue

HSDPA Channels



HS-PDSCH, HS-DSCH, HS-SCCH and HS-DPCCH (UL).

HS-DSCH is mapped on to HS-PDSCH - which carries data to the UE, and HS-SCCH carries the UE identity and instructions to decode the information carried in HS-PDSCH.

HS-DPCCH carries ACK/NACK and CQI information from UE to network (Node B).

AMC & HARQ explained

Adaptive Modulation and Coding (AMC):
HSPDA standard ensures that highest possible data rate is acheived for all users regardless of whether they are close to the base station or far off. This is done using ACM. For HS-DSCH, the transport format, including the modulation scheme and code rate, can be selected based on the downlink channel quality. The selection of transport format is done by the MAC-HS located in Node B and is based on channel quality feedback reported by the UE. The spreading factor cannot change but the coding rate can change between 1/4 and 3/4. The higher coding rate reduces the number of errors. Also the standards support multicodes. This means that upto 15 codes can be allocated to a UE.

Hybrid Automatic Repeat Request (HARQ):
In case of ARQ, the receiving system on receipt of data checks the CRC. If the CRC is the same as that received in the message ACK is sent back to the sender. In case if CRC does not match then NACK is sent back and the packet discarded. In case of HARQ, this method of CRC checking is improved based on the following two things.

Chase Combining: In this when an error is detected in CRC, NACK is sent back but the packet is not discarded. It is stored. In case the re-transmitted packet is again erroneous then the previous and current poacket is combined in an attempt to recover from errors. Each time the packet is resent, the same scheme is applied. Eventually the error will be either resolved or maximum number of retries is reached. In that case higher layer protocols will deal with the error.

Incremental Redundancy (IR): IR is similar to Chase combining but the redundant information that was not transmitted earlier is also included to improve the chances of reception without errors or with enough errors removed so as to allow combining with the previously stored packet and resolve the errors.

Fast Cell Site Selection (FCSS):
When the UE moves between the cells, it is possible that it would be served by different cells. Hence the UE will construct a list of Active Set (the term Active Set is incorrect and the term that will be used eventually is "Eligible Set") Cells that it can use at any one time. The mobile will indicate on HS-DPCCH as to which one is the best cell for DL transmission. The serving cell then decides the modulation and coding scheme to be used for the mobile and in addition may code multiplex multiple mobiles within that HSDPA frame. To Simplify this procedure, it is further subdivided into Intra-Node B FCS and Inter-NodeB FCS.