S - Communication Technology Laboratory

Mobile Communications:
Technology and QoS
Course Overview
!
Marc Kuhn, Yahia Hassan
[email protected] / [email protected]
Institut für Kommunikationstechnik (IKT) Wireless Communications Group
ETH Zürich
1
MCTQ:
Overview of the Course
(a few selected slides per chapter)
!
Dr.- Ing. Marc Kuhn !
[email protected] !
Institut für Kommunikationstechnik (IKT), !
Wireless Communications Group !
ETH Zürich!
!
2
Contents
Introduction!
Wireless Channel !
Mobile Communication!
Wireless Networks!
Quality of Service – QoS !
Future Technologies
3
Contents
Introduction!
Wireless Channel !
Mobile Communication!
Wireless Networks!
Quality of Service – QoS !
Future Technologies
4
Wireless Channel
Propagation Channel !
Maxwell equations, system functions of wireless channels!
Multipath Propagation !
Path loss!
Doppler Effect!
Channel Characterization, Channel Models!
Fading, delay spread, Doppler spread, coherence time and bandwidth,
channel models !
Antennas
5
Wireless Channel: Observations
Channel strength (attenuation) and thus SNR at Rx
varies !
depending on the location (space-selective fading)!
over time (time-selective fading)!
over frequency (frequency-selective fading)!
Bandwidth limited!
Shared medium!
interference
6
Basic Propagation Mechanisms
Reflection!
Propagating electromagnetic wave impinges on object with very large
dimension compared to wavelength !
Reflection e.g. from buildings and walls (or from surface of earth)!
Diffraction!
Radio path between Tx and Rx obstructed by a surface that has sharp
irregularities!
Scattering!
Between Tx and Rx: objects with dimensions small compared to the
wavelength
7
Multipath Propagation: LocationDependent Fading
|rTX| [dB]
Position A
r2
r1
r3
Position B
at a given frequency f1
r2
r1
r4
rTX
8
location x
rTX
Wireless Channel
Large-scale fading!
➡
Relevant to cell-site planning
Received power decreases with distance r!
e.g. free space: 1/r² !
can even be faster due to shadowing and scattering effects!
!
Small-scale fading!
➡
Relevant to design of communication systems
Variation of signal strength over distances of the order of the carrier
wavelength, due to constructive and destructive interference of multi-paths!
Doppler spread, coherence time (e.g. due to velocity of mobile)!
Delay spread, coherence bandwidth (lengths of shortest and longest
path)
9
X
1/∆tmax
=
f
f
Narrowband System
|hc(t )|
|hs(t )|
f
|h(t )|
=
∆tmax
t
t
t
Narrowband system
|Hc(f )|
|Hs(f )|
|H(f )|
X
1/∆tmax
=
f
|hc(t )|
f
f
|hs(t )|
|h(t )|
=
∆tmax
t
t
t
Figure 6.4 Narrowband and wideband systems. HC (f ), channel transfer function; hC (τ ), channel impulse
response.
[Molisch, “Wireless Communications“]
Reproduced with permission from Molisch [2000] © Prentice Hall.
10
be modeled. Note that any real channel is frequency selective if analyzed over a large enough
bandwidth; in practice, the question is whether this is true over the bandwidth of the considered
system. This is equivalent to comparing the maximum excess delay of the channel impulse response
with the inverse system bandwidth. Figure 6.4 sketches these relationships, demonstrating the
variations of wideband systems in the delay and frequency domain.
We stress that the definition of a wideband wireless system is fundamentally different from
the definition of “wideband” in the usage of Radio Frequency (RF) engineers. The RF definition
Wideband (or Broadband) System
Wideband system
|Hs(f )|
|Hc(f )|
|H(f )|
X
1/∆tmax
=
f
f
|hc(t )|
f
|hs(t )|
|h(t )|
=
∆tmax
t
t
t
Narrowband system
|Hc(f )| [Molisch,
“Wireless
Communications“]
|H (f )|
|H(f )|
s
X
1/∆tmax
f
=
11
f
f
Quasi-Static CIR
Quasi-static, h(t, τ) varies only slowly over time: !
Variable t parameterizes the impulse response: which (out of a large
ensemble) impulse response h(τ) is currently valid
From [“Wireless Communications: Principles & Practice” T. Rappaport]
12
Multipath Propagation, Narrowband
Fading
Multipath propagation:!
constructive and destructive
interference!
mean
random fluctuations of receive power –
(small-scale) Fading!
strong influence on quality of the
transmission
13
Contents
Introduction!
Wireless Channel !
Mobile Communication!
Wireless Networks!
Quality of Service – QoS !
Future Technologies
14
Mobile Communication
PHY Layer !
OFDM !
MIMO !
Receiver structures !
MAC Layer !
MAC: IEEE 802.11, .11e
15
OFDM
Continuous-time vs. discrete-time model !
419
Orthogonal Frequency Division Multiplexing (OFDM)
Channel
Transmitter
c0, i
(a)
Data
source
S/P
conversion
Receiver
c
0, i
e j0
e
j0
c
1, i
c
e
s(t )
j 2π(W/N)t
H
Hs(t )
1, i
e j 2π(W/N)t
c
c
N 1, i
j 2π(N 1) (W/N)t
e
e
S/P
conversion
Data
sink
0, i
c1, i
IFFT
cN 1, i
P/S
conversion
N 1, i
c
0, i
Data
source
Data
sink
j 2π(N 1) (W/N)t
c
(b)
P/S
conversion
P/S
s(t )
c1, i
H
Hs(t )
S/P
FFT
c
N 1, i
Figure 19.2 Transceiver structures for orthogonal frequency division multiplexing in purely analog technology
[A. Molisch, “Wireless Communications]
(a), and using inverse fast Fourier transformation (b).
An alternative implementation is digital . It first divides the transmit data into blocks of N
symbols. Each block of data is subjected to an Inverse Fast Fourier Transformation (IFFT), and
then transmitted (see Figure 19.2b). This approach is much easier to implement with integrated
circuits. In the following, we will show that the two
16approaches are equivalent.
Let us first consider the analog interpretation. Let the complex transmit symbol at time instant
OFDMA
Distributed OFDMA mode
User 1
2
3
OFDM sub-carriers
Localized OFDMA
mode
17
Diversity Techniques
Tx Diversity: Alamouti Code (ST-Code)
h 1,1
!  Vectors: elements in spatial domain
s1
⎛ s
1
s1 = ⎜
⎜⎝ −s2*
r1
h 1,2
s2
⎞
⎟
⎟⎠
⎛ s ⎞
2
s2 = ⎜ * ⎟
⎜⎝ s1 ⎟⎠
!  Matrix S: 2 vectors in 2 time-slots
⎛ s
1
S = ⎡⎣s1s2 ⎤⎦ = ⎜
⎜⎝ −s2*
Assume channel const. for 2 time slots:
r1 (1) = h 1,1 s1 − h 1,2 s2* + w1 (1)
s2 ⎞
⎟
s1* ⎟⎠
*
* *
r1 (2) = h 1,2 s1* + h 1,1 s2 + w1 (2) → r1* (2) = h1,2
s1 + h1,1
s2 + w1* (2)
!  Orthogonalize decision variables
d(1) = h r (1) + h r (2) = h 1,1 s1 + h 1,2 s1 + n1
!  Two-fold diversity !
2
2
*
d(2) = −h1,2
r1 (1) + h1,1r1* (2) = h 1,1 s2* + h 1,2 s2* + m1 !  One symbol per time slot (more
*
1,1 1
*
1,2 1
2
2
efficient!)
Diversity, MIMO
Marc Kuhn
18
22
MIMO
Multiple Input Multiple Output – MIMO
RX
TX
Telatar, Foschini:
⎧⎪
⎡ ⎛
⎞ ⎤ ⎫⎪
ES
C = E ⎨log 2 ⎢det ⎜ I M +
HH H ⎟ ⎥ ⎬
⎠ ⎥⎦ ⎭⎪
⎢⎣ ⎝ R M T N 0
⎩⎪
MT: number of TX antennas,
MR: number of RX antennas.
Diversity, MIMO
Marc Kuhn
19
33
Capacity of MIMO Channels: Perfect CSIT
!  With perfect CSIT:
- 
Tx combining to orthogonalize MIMO channel (multiply with unitary matrix V)
Tx signal : s = Vs
- 
where H = USV H
Tx power per Eigenvalue has to be optimized (Water-filling algorithm)
=> choose optimal γi (energy allocated to sub-channel i) to maximize capacity
( ),
γ i = E si
2
N
∑γ
for i = 1, 2, ..., N
i
= MT
i=1
wi!
si!
! λ
i
yi!
+!
yi =
CpCSIT
ES
λi si + ni
MT
⎡N
⎛
⎞⎤
ES
H
= max
log
1+
λ
HH
⋅
γ
⎢
∑ 2 ⎜⎝ M N i
i⎟ ⎥
N
⎠ ⎥⎦
∑1 γ i = M T ⎢⎣ i=1
T 0
{
Diversity, MIMO
Marc Kuhn
20
}
41
Multi-User MIMO
Uplink: Multiple Access Channel (MIMO-MAC) !
!
!
!
Downlink: Broadcast Channel (MIMO-BC)
21
WLAN IEEE 802.11
MAC Sublayer: DCF
transmit, if medium is free
>= DIFS
DIFS
Medium busy
DIFS
Contention Window
PIFS
SIFS
Backoff-Window
Slot time
Next
Frame
Decrement Backoff Timer as
long as medium idle
Defer access
CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance):
!  Channel access:
!  If WM seems to be free for a time >= DIFS, STA transmits immediately
!  If WM busy, STA waits until the end of the ongoing transmission and
starts Backoff Procedure
!  After this the status of the channel is checked again
MCTQ: Wireless Networks, 802.11
Marc Kuhn
Wireless Networks, 802.11
22
|!
08.10.14
|! 50
Contents
Introduction!
Wireless Channel !
Mobile Communication!
Wireless Networks!
Quality of Service – QoS !
Future Technologies
23
Wireless Networks
Current (and future) wireless networks:!
How do they work?!
For which services are they used?!
Cellular Networks!
GSM!
UMTS!
LTE, LTE-Advanced !
WLAN IEEE 802.11n
24
Cellular Networks
Mobile Communication
!  Omnipresent
! 
9.9 Mio. SIM cards in CH
(2012)
! 
99.9 % of Swiss population
covered
! 
Exponential increase in data
traffic
!  Different standards
(GSM, UMTS, LTE, ... )
(2G, 3G, 4G)
Cellular Networks
11
25
Cellular Networks
Cellular Wireless: max. Downlink Rates
1000
Peak data rate [Mbit/s]
1000
84.4
100
150
14.4
10
0.4736
1
0.1152
0.384
0.1712
0.1
0.0096
0.01
ed
va
nc
LT
E
LT
EAd
SP
A+
H
PA
SD
H
TS
U
M
G
E
ED
S
G
PR
SC
H
G
SM
C
SD
SD
0.001
!  Techniques to achieve this almost exponential growth in peak rate
!  Closer look on LTE and LTE-Advanced
Cellular Networks
12
26
Cellular Networks
Structure of Cellular Networks
Mean Rate Rmean(SINR), DL, with BS interference
22e+09
Gbit/s
1.8e+09
−1500
1.6e+09
1.4e+09
1.2e+09
1e+09
8e+08
−1000
6e+08
4e+08
y Position [m]
−500
200
Mbit/s
2e+08
0
500
1000
1500
−1500
−1000
−500
0
500
1000
1500
10
Mbit/s
1e+07
x Position [m]
Cellular Networks
16
27
Coordinated Multi Point - CoMP
28
Contents
Introduction!
Wireless Channel !
Mobile Communication!
Wireless Networks!
Quality of Service – QoS !
Future Technologies
29
Quality of Service - QoS
What does QoS mean?!
How is QoS support implemented in wireless networks?!
Which problems do occur? !
Theoretical analysis of QoS at PHY and MAC of wireless systems!
How can we measure QoS? !
End-to-End QoS Measurements!
Statistical evaluation of QoS measurements!
Benchmarking (drive tests, methods)
30
PHY QoS KPIs
MIMO: Outage Probability for Outage Rate 6
0
10
(2x2) MIMO
−1
10
SISO: CDF of channel capacity ; Rayleigh fading
1
−2
Pout
(3x3) MIMO
(2x3) MIMO
Cumulative Distribution Function
10
−3
10
(3x2) MIMO
−4
10
−5
10
0
5
10
15
20
S / N [dB]
0.9
0.8
0.7
0.6
0.5
0.4
SNR = [0, 5, 10, 15, 20] dB
0.3
0.2
0.1
0
0
2
4
6
8
Capacity [bit/channel use]
Outage Rate: 2 bit/ channel use!
31
10
12
MAC QoS KPIs
Example: IEEE 802.11 MAC
32
Quality of Service - QoS
What does QoS mean?!
How is QoS support implemented in wireless networks?!
Which problems do occur? !
Theoretical analysis of QoS at PHY and MAC of wireless systems!
How can we measure QoS? !
End-to-End QoS Measurements!
Statistical evaluation of QoS measurements!
Benchmarking (drive tests, methods)
33
E2E QoS Measurements
Call Stability ( Comparison of the last 4 quarters)
8,0%
7,0%
6,0%
Call Drop Rate [%]
5,0%
4,0%
3,0%
2,0%
1,0%
0,0%
-1,0%
34
Module 1
Module 2
Module 3
Module 4
A Q2/04
0,6%
2,1%
0,4%
0,7%
A Q3/04
0,3%
1,9%
0,2%
0,5%
A Q4/04
0,4%
2,0%
0,2%
0,6%
A Q1/05
0,4%
1,6%
0,1%
0,8%
B Q2/04
0,2%
1,3%
0,1%
0,2%
B Q3/04
0,3%
1,1%
0,2%
0,5%
B Q4/04
0,4%
1,2%
0,1%
0,4%
B Q1/05
0,5%
0,9%
0,1%
0,4%
C Q2/04
1,4%
5,9%
0,7%
0,5%
C Q3/04
1,8%
3,9%
0,4%
0,5%
C Q4/04
0,9%
3,1%
0,4%
0,4%
C Q1/05
1,2%
3,2%
0,2%
0,2%
D Q2/04
1,5%
4,0%
0,8%
0,5%
D Q3/04
1,8%
2,8%
0,4%
0,2%
D Q4/04
1,5%
4,0%
0,2%
0,5%
D Q1/05
1,4%
2,5%
0,0%
0,4%
Call Stability ( all Modules)
4.5%
Call Drop Rate [%]
4.0%
3.5%
3.0%
2.5%
2.0%
1.5%
1.0%
0.5%
0.0%
-0.5%
Module 1
Module 2
Module 3
Module 4
A
0.4%
1.6%
0.1%
0.8%
B
0.5%
0.9%
0.1%
0.4%
C
1.2%
3.2%
0.2%
0.2%
D
1.4%
2.5%
0.0%
0.4%
Won Pairwise comparisons: Coverage Quality ()
Won Pairwise comparisons: Call Setup Success Rate
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
Module 1
Module 2
Module 3
Module 4
All Modules
A
0
2
-2
0
0
B
0
2
2
0
C
1
-2
2
0
1
D
-1
-2
-2
0
-5
4
35
Contents
Introduction!
Wireless Channel !
Mobile Communication!
Wireless Networks!
Quality of Service – QoS !
Future Technologies
36
Future Technologies
Base station or user cooperation!
Relaying !
Interference alignment !
...
37

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