Scrambling Code in WCDMA

-

Let's suppose you are a NodeB. You will getting various signals from many different users (UEs) all at the same time. Then how would you differentiate the incoming signals into separate users at the very low level of your hardware ?. Of course you can figure out exactly which user you are dealing with at higher layer with various type of user ID (UE ID), but my question is how to figure out each user at PHY layer ?

Now let's assume that you are a UE. You may be hearing many signals from multiple NodeBs simultaneously. Then how would you differentiate the incoming signals into separate NodeB at the very low level of your hardware ?

The answer to both of the question is same. It is "Scrambling Code". By using the scrambling code, NodeB can separate signals coming simultaneously from many different UEs and UE can separate signals coming simultaneously from many different NodeB.


Now let's look into how/where the scrambling code works. Following illustration shows the procedure about the data processing in physical layer.  As you see in the following diagram, "Scrambling" happens at the chip rate of the signal processing. Since the chip rate of the scrambling code is the same as the chip rate of the chanelization code scrambling does not change the signal data rate.


A specific bit sequence which is used for scrambling is called 'Scrambling code'.

There are two types of scrambling codes : long scrambling code and short scrambling code. Long scrambling code(38400 chips) derived from Gold codes and short codes (256 chips) derived from S(2) codes.  
Then which type of scrambling code we use ?.
In downlink, only long codes are used.

In uplink direction long codes are used for node B using Rake reciever and short codes are used for NodeB using multiuser detection or interference cancellation recievers. With short codes the implementation of cyclic processing structure is simpler.

Popular posts from this blog

SCFT - Single Cell Function test

-
Single Cell Function test SCFT is for verifying whether individual BTS works well or not, by making a single cell function test of BTS hardware and software. Essential items to be tested are as follows: 1) BTS Transmitter Output Measurement Test 2) Initial parameter establishment (Pilot PN/System ID/Site ID/Frequency, Neighbor List) 3) Call Origination and Termination Test 4) Softer Handoff Test/Antenna installation check (Direction, Tilt, Transmission Line) 5) Single Cell Coverage Test 6) Noise Floor Test 7) Parameter check.
Read more

Troubleshooting for GSM KPIs (SD Block & SD Drop)

-
KPIs to be monitored: ·             SD Blocking ·             SD Drop SDCCH Channel: ·    SDCCH channel is a dedicated channel which is using for LAC updation, Call Setup, SMS in Ideal mode. It works in UL & DL SD Blocking: ·    SD Blocking means that you are not getting SD resource for the call origination. When MS connects with Network then RACH and AGCH are provided. After AGCH, SDCCH is provided but if SDCCH is not provided at this time due to some problem or due to unavailable of SD by BSC. KPI Formula in Ericsson: ·             SDCCH CONGESTION = (CCONGS / CCALLS) * 100 ·             CCONGS - Congestion counter. ·             CCALLS - Channel allocation attempt counter (on SDCCH). Reason for SD Blocking: ·             LAC Boundary ·             High Volume of SMS ·             SD utilization is high ·             Time Slot fault
Read more

PS core network

-
Image
The PS core network consists of two parts, the traditional General Packet Radio Service (GPRS) core network and the new Evolved Packet System (EPS) core network. The PS core network connects mobile subscribers to Packet Data Networks (PDNs) such as the Internet, corporate networks or operator services networks.  a functional overview of the PS core network. Logical entities and interfaces are shown in black and form a 2G/3G network, while the blue boxes and lines in Figure  show the LTE/EPC related parts. The LTE/EPC network can be regarded as an extension and evolution of existing 2G/3G networks. From a node implementation perspective, there is no strict border between the two networks. The corresponding logical entities of GPRS and EPS networks can be deployed concurrently in Ericsson PS core nodes, such as the SGSN-MME and EPG; these are marked in red. In addition, Ericsson GPRS nodes can be upgraded with EPC functionality by software only. Network evolution is support
Read more