1. Johan Montelius jm@sics.se
Radio Access
Johan Montelius

2. Shannon C = W x log2(1 + S/N)
The capacity [C] in bits/s is directly proportional to the available bandwidth [W] and
log2 proportional to the signal to noise ratio [S/N].

3. bandwidth & power

4. Attenuation in open space
Sr = S0/4r2
The signal strength at a distance [Sr] is directly proportional to the sending strength [S0] and indirectly proportional to square of the distance [r]

5. Real life
In urban environment the signal strength is proportional to 1/rk where k = 1,6 … 3,8

6. Distance costs

7. Too bad for broadcast but good for cellular systems
Not a problem
detectable
good quality

8. What is interference

9. Rules of thumb Bandwidth Power Noise
most important factor to increase capacity
Power
will buy you distance but at a high cost
Noise
your own signal can be the worst problem

10. Divide the resources Space Frequency Time Code
systems ”far” apart don’t interfere with each other
Frequency
modulate the signal to use a specified frequency band
Time
synchronize and allocate time slots
Code
Information coding

11. National/International regulations
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
MSS
ITU
IMT 2000 EU
GSM 1800
UMTS
DECT
MDS US
PCS
Jp/Ko
IMT 2000
China
GSM 1800
IMT 2000

12. Frequency division
By modulating a carrier frequency, the radiated power can be limited to a specified frequency range.
The width of the range is the bandwidth of the carrier.
A guard band is needed to protect adjacent carriers.

13. Frequency planning A B C 3 cells per site
typically used in urban environment

14. Frequency planning 4 sites, 3 cells per site minimum distance
12 carriers needed A D B E C F A J G H K I L

15. Time division Enabled by faster processors.
A carrier is divided into time slots.
Each channel is allocated a time slot.
A guard period is needed between adjacent time slots

16. Timing advance
A sender must adjust its transmission to meet the time slot at the receiver. The farther away the earlier you send . The base station will tell you if your late or early. a b B A

17. Locating a mobile terminal

18. What is left ? when bandwidth is fixed and power is limited
do the best modulation possible

19. Modulation frequency modulation amplitude modulation phase modulation
combination of above
… no modulation ?

20. Wireless systems Often use a phase modulation
Could change modulation depending on quality of signal
Spectral efficiency
up to 2 bits raw data per Hz under good conditions
aprx 0,5 to 1 bit user data per Hz
limited by signal to noise ratio

21. How do we compare? What is the maximum user capacity?
What is the maximum capacity of a system?
How many carriers do we have?
What is the total capacity of a carrier?
How many carriers can be used at any given point?

22. GSM Each duplex carrier is 2x200 KHz wide 900 1800 1900 (in the US)
up MHz down MHz
124 duplex carriers
2x25MHz in total
1800
up MHz down MHz
374 duplex carriers
2x75MHz in total !!!!!
1900 (in the US)
up MHz down
2x60MHz in total

23. GSM Time division Gaussian Minimum Shift Keying (GMSK) HSCSD
8 time slots per carrier
one carrier up one carrier down
Gaussian Minimum Shift Keying (GMSK)
user bitrate 9,6 kb/s or 14,4 kb/s per timeslot
raw bitrate 272 kb/s per carrier
HSCSD
Two or more time slots

24. Up and down 1 2 3 4 5 6 7
down up
The up link is delayed 3 slots in order to give the terminal time to adjust to the new frequency. Time slots 5 and 6 can be used to listen for better frequencies.

25. GPRS Dynamically allocate time slots Data and voice can be combined
normally 1:4 one up, four down
Data and voice can be combined
Coding schemes (user data rates)
CS 1: 9,05 kb/s total 72,4 kb/s
CS 2: 13,4 kb/s total 107,2 kb/s
CS 3: 15,6 kb/s total 124,8 kb/s
CS 4: 21,4 kb/s total 171,2 kb/s

26. EDGE Enhanced data rate for GSM Evolution
Change the modulation to 8-PSK i.e. 3 bits per symbol
User data rate
22,8 kb/s to 69,2 kb/s
Total of 553 kb/s
don’t move

27. UMTS/WCDMA Each paired carrier is 2x5MHz
155 MHz in total
Unpaired carriers can be used using time-division duplex mode (TDD)
A typical operator
Two or three paired, one unpaired
Up to six operators share the spectrum

28. ISM 2.4 GHz Industrial, Scientific and Medical
US – ,5MHz in total
Japan 2400 – ,7MHz in total
Open for anyone, no license
Limitation on power < 0.1W (<1W US)
Using a spread spectrum technique

29. Spread spectrum Why spread the signal over a wider spectrum?
more robust, will survive if part of the spectrum is noisy
will allow other systems to operate in the same environment
Two techniques
frequency hopping
direct sequence

30. Frequency Hopping divide the spectrum into separate carriers
In ISM, FCC regulated at least 70 carriers
transmit and hop
In ISM, FCC regulates < 400 ms
a code determines where to hop
how do we synchronize?
low cost, low power, very robust

31. Direct Sequence
Increase the bandwidth by sending a pattern, chipping sequence, at a higher bitrate
sequence can be static or dynamic
dynamic patterns are used in CDMA
high bitrate, robust

32. Bluetooth 1.1 Frequency hopping, GFSK modulation
Gaussian Frequency Shift Key
79 carriers of 1 MHz, 1600 hops per s
Power
Class 1: 20dBm (100mW) range aprx 100m
Class 2: 4dBm (2,5 mW) range aprx 10m
Class 3: 0dbM (1 mW) range aprx 10 cm
Master & Slave
Master determines hopping sequence
Capacity 712 Kb/s per channel

33. 802.11b DSSS, BPSK (1Mbps) QPSK (11Mbps) ISM 2.4 Carrier
US 11 carriers
Europe (except France and Spain) 13 carriers
Japan 14 carriers
Carrier
22 MHz wide
can use 3 carriers without overlap!

34. 802.11b 1 Mb/s using BPSK 2 Mb/s using QPSK 5,5 and 11 Mb/s
Barker spread sequence of 11 bits
2 Mb/s using QPSK
Barker sequence of 11 bits (22 Mb/s raw data)
5,5 and 11 Mb/s
QPSK, same as for 2Mb/s
complementary code keying
1,375M symbols/s
each symbol is 8 bits long (11 Mb/s raw data)
each symbol represents 4 or 8 bits

35. 802.11b 11 Mb/s 8 b/symbol 8 chips/symbol 1,375 Msymb/s QPSK
1 Mb/s 1 b/symbol chips/symbol 1 Msymb/s BPSK

36. Code division Same frequency can be used No cell planning
How do we decode the message?

37. Code division: coding 1 d1 d2 message di -1 1 code cik -1 1
Zik= dik * cik
out zik -1

38. Code division: decoding1
out zik -1 1
code cik -1 S m 1
di =
zikcik m
k = 1 1
d1 =
(-1 –1 – 1 –1 – 1 – 1 –1 – 1) = -1 8

39. Code division: multiple senders
Da =
Ca =
Za =
Db =
Cb =
Zb =

40. Code division Za = -1-1-1+1-1+1+1+1+1+1+1-1+1-1-1-1
Zb =
Zab=
Zab=
Ca =
ZCa=
Sa= /8 = /8 = +1

41. UWB
Ultra wide band
More than 1.5 GHz or 20% of central frequency
Use low power, low enough to disappear in noise level of other systems
Compensate by using large bandwidth, up to several GHz
Distance is, due to low power, limited < 10 m

42. Shannon revisited
Shannon’s theorem sets a limit for one receiver listening to one message.
What happens if we have several channels open, multiple receivers.
Is there a limitation on capacity in space?

43. WCDMA
5 MHz carrier
QPSK modulation
3,84 Mcps chipping rate