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ELEC ENG 3108 Telecommunications Principles
Assignment 3: Wideband CDMA
Due 23:59 Monday 7 November – via MyUni only. This assignment is worth 50% of your final grade.
What to submit
? Your working and results
? Some of your marks will be allocated to discussion, insight and original experimentation or
analysis. Your report is expected to be written to a professional standard and demonstrate
your personal critical insight.
Question 1 (15/50): WCDMA Planning
Part 1: Implement the Walfisch-Ikegami path-loss model as a function in Matlab. Two functions are
required:
(a) Given environmental parameters and distance, calculate the mean path loss
(b) Given environmental parameters and the maximum mean path loss, calculate the maximum
coverage distance
Part 2:
Using the link budget data given in the notes and these link budgets as a guide, use your path loss
model to explore link budgets under different scenarios. You should extend your software to
consider data rate, indoor versus outdoor versus vehicular use, etc.
Part 3:
Consider the peak up-link capacity of a third generation W-CDMA cell carrying three types of traffic
with the following characteristics:
Service Bearer data
Rate Rj
Activity
Factor vj
Bit Energy to Noise
Ratio (Eb/N0)j
Number of Channels in
use
Video
phone
64 kbit/s 100% 1dB 3
File
upload
384 kbit/s 25% 3dB 4
Voice 12.2 kbit/s 67% 1dB Unknown
? Interference ratio from other cells i=0.65
? Maximum noise rise = 3 dB
? Assume that signalling occupies the equivalent of one voice circuit
? Chip Rate W=3.840 Mchip/s
a) Calculate the Load Factor for each of the 3 services.
b) Hence determine the maximum number of channels available for voice on this cell and calculate
the aggregate user data rate on the uplink.
c) Assuming that the following channel data rates are used for each application and that all three
services are in use as above, determine the number of Orthogonal Variable Spreading Factor codes
available for voice circuits.
– Video phone: 240 kbit/s
– File upload: 480 kbit/s
– Voice: 30 kbit/s (6 marks)
d) How many voice circuits would be available if the cell were only used for voice? Also calculate the
aggregrate up-link user data rate in this case.
Question 2: WCDMA Implementation (35/50)
The aim of this question is to decode the WCDMA signal in the attached Matlab file. The signal
consists of
? An unknown number n of blocks, each of 38400 chips (10ms), a total of 10n ms of signal
? A normalised noise-free single path downlink signal (perfect path assumption)
? A 38400 chip scrambling code which is the real part only of one of the 512 primary downlink
scrambling codes Sdl,n where n is in [0..511] as defined in the standard. The actual
scrambling code used is unknown.
? A strong common pilot channel under the scrambling code. The power level of the pilot
channel is unknown.
? An unknown number of traffic channels, each with a spreading factor between 16 and 512
containing ASCII text. The actual spreading codes used are unknown.
Your challenge is to:
? identify the scrambling code and signal strength of the Pilot CPICH
? identify the valid channel codes and their respective signal strength
? decode the traffic channels and read the enclosed message
? from what you learn, demonstrate some open-ended investigation. It is quite acceptable to
collaborate and for different members of the class to explore different aspects of WCDMA
including multipath, additive noise, encoding, etc.
Some things you need to know:
? The scrambling codes, OVSF codes and common pilot channel (CPICH) have been generated
consistent with 3GPP Technical Specification 25.213 Release 4. This standards document is
available on the MyUni website. Pay particular attention to sections 4.3.1, 5.2.1 and 5.2.2.
? The only common channel is the CPICH. No other common channels (such as synch channel
etc) are in the signal. So you can identify the scrambling code by correlating the 512 primary
codes against the signal to see which one has the highest correlation. Only the real
component of the downlink scrambling code is used.
? The signal is synchronised – that is the first sample corresponds to the beginning of a 38400
chip frame.
? The traffic channel is modulated with BPSK. A positive correlation (+1) corresponds to “1”, a
negative correlation (-1) to “0”. No correlation (0) indicates that the channel is not present.
? Valid traffic channels contain only 8-bit ASCII characters, beginning with the most significant
bit. The first two characters are an ASCII representation of numerical digits, corresponding
to a number between “01” and “99”. The third character is a space. This will be sufficient to
identify valid channels and to put the traffic channels in the correct order to read the
message.
? The message in the signal is up to 99 lines of ASCII text, each of up to 1000 characters
(including padding in the form of spaces (character 32)) and beginning with the 2-digit and
space header. Control characters such as Line Feed (10) and Carriage Return (13) may be
included.
? The traffic channels all begin at the start of the first frame but do not continue for the entire
signal. In particular, signals with fast codes will finish early.
Marking:
? 20 marks will be based on your technical answers, including your code, signal analysis and
the encoded message.
? 5 marks will be based on how well you explain your approach.
? 10 marks will be based on any additional detail, analysis or experimentation you describe in
your report. For example, you might want to explore how the exercise compares with the
real world (added noise and interference, multipath etc) and see how your decoder works
when you add noise to the signal. You might also like to discuss computational complexity.
Remember, I’m not just looking for some code and some numbers. I want a clear description of how
you solved the problem and some exploration of WCDMA using the tools provided by this
assignment.
Don’t panic! The standard is very explicit in its description of how to generate the scrambling and
channelisation codes. One important thing to note is that Matlab starts its vector indices from 1; the
standard is consistent with C and starts its vector indices from 0, so you’ll need to allow for this.
Some helpful code to get started:
function string=bits2str(bitsequence);
bitsequence=(bitsequence>0.001);
% note: +1 = binary 1, -1 = binary 0; 8-bit ASCII, convert to
% 0 or 1
block=char(reshape(bitsequence,8,length(bitsequence)/8)+48)’;
string=char(bin2dec(block));
end
%——————–
function data=recover(spread,codenumber,tx,scramblecode,nbytes);
data=zeros(1,8*nbytes);
channel=ovsf(spread,codenumber); %you’ll need to write the ovsf fn
for j=1:nbytes*8;
k=(j-1)*spread+1;
data(j)=sum(tx(k:k+spread-1).*scramblecode(1+mod(k-1,38400):…
1+mod(k+spread-2,38400)).*channel);
end
The signal file includes the signal (transmitsignal) and also scrambling code 0
(samplescramblingcode0) so that you can verify that your scrambling code function is working
properly.