无线通信基础双语教学课件.ppt
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chap03 Communication Networks 无线网络通信 英文课件
Message is broken into a series of packets Each node determines next leg of transmission
for each packet
Phases of Circuit Switching
Circuit establishment
Priorities can be used
Disadvantages of Packet Switching
Each packet switching node introduces a delay Overall packet delay can vary substantially
This is referred to as jitter Caused by differing packet sizes, routes taken and
varying delay in the switches
Each packet requires overhead information
Includes destination and sequencing information Reduces communication capacity
End devices that wish to communicate Each station munications Network:
A collection of switching nodes
Switched Network
packet Emulates a circuit in a circuit switching network
but is not a dedicated path
for each packet
Phases of Circuit Switching
Circuit establishment
Priorities can be used
Disadvantages of Packet Switching
Each packet switching node introduces a delay Overall packet delay can vary substantially
This is referred to as jitter Caused by differing packet sizes, routes taken and
varying delay in the switches
Each packet requires overhead information
Includes destination and sequencing information Reduces communication capacity
End devices that wish to communicate Each station munications Network:
A collection of switching nodes
Switched Network
packet Emulates a circuit in a circuit switching network
but is not a dedicated path
无线通信基础双语教学课件16
➢Channel Partitioning (FDMA TDMA CDMA) ➢Taking Turns (Taking Ring) ➢Random Access (Aloha CSMA)
Orthogonality can be mechanized using a. Space division multiple access (SDMA) DMA） c. Time division multiple access（TDMA） d. Code division multiple access（CDMA）
A borrowing option may be considered, if all of a cell’s own channels are already occupied and the neighboring cell has spare channels.
In DCA, voice channels are not allocated to different cells on a permanent basis.
✓ Transmission from any node is received by other nodes
Node 3
Node 2 Node 1
Shared Multiple Access Channel
Node 4 Node N
5.1 Multiple access in a radio cell 5.2 Random Access 5.3 Conflict-free multiple access technologies 5.4 Spectral efficiency
Transmission in the uplink have the following attributes:
Orthogonality can be mechanized using a. Space division multiple access (SDMA) DMA） c. Time division multiple access（TDMA） d. Code division multiple access（CDMA）
A borrowing option may be considered, if all of a cell’s own channels are already occupied and the neighboring cell has spare channels.
In DCA, voice channels are not allocated to different cells on a permanent basis.
✓ Transmission from any node is received by other nodes
Node 3
Node 2 Node 1
Shared Multiple Access Channel
Node 4 Node N
5.1 Multiple access in a radio cell 5.2 Random Access 5.3 Conflict-free multiple access technologies 5.4 Spectral efficiency
Transmission in the uplink have the following attributes:
【可编辑全文】无线通信基础PPT课件PPT47页
变和衰落，这就是无线电波传输中的多径衰落。
X 第11页，共47页。
1.1.2 无线电波的传播特性
第 11
页
3、无线电波传输中的多径衰落 多径衰落可能引起两种特殊的选择性衰落： （1）频率选择性衰落
（2）时间选择性衰落
X 第12页，共47页。
1.1.2 无线电波的传播特性
第 12
页
4、电离层的结构及其对短波信道的影响
由于受到周围建筑物以及地面的反射和散射作用， 往往使同一波源发出的信号沿多条不同的传输路径， 以不同的时间到达接收机。这些经不同路径到达的波， 称为多径波。由于不同路径的信号的传播距离及传播时延
不同，到达接收机时的相位也就不同，从而使接收到的信 号的幅度有时因同相叠加而增强，有时又因反相叠加而减 弱。这样，接收信号的幅度就会产生剧烈的变化，造成畸
X 第3页，共47页。
1.1.1 无线电波段的划分
第 3
页
本书讨论的无线通信覆盖的无线电波频率范围
主要是HF、VHF、UHF和SHF波段。
X 第4页，共47页。
1.1.1 无线电波段的划分
第 4
页
分米波段 ，特高频（UHF），波长为1m-10cm
微 波 厘米波段，超高频（SHF），波长为10-1cm 频 段
1.3.1 基本概念
第 32
页
3、基带传输与频带传输
基带信号：由信源直接生成的信号。
频带信号：基带信号经调制后生成的信号。
在数字通信系统中，在传输距离不太远的情况下，将来自
信息源的数字基带信号直接传输，称为数字基带传输。
将数字基带信号经过载波调制，把频谱搬移到高频 处再传输，这种传输称为数字频带传输。
路径衰耗与距离的n次方成比例，其中n称为路径衰 耗指数，不同传输环境取不同的值。
X 第11页，共47页。
1.1.2 无线电波的传播特性
第 11
页
3、无线电波传输中的多径衰落 多径衰落可能引起两种特殊的选择性衰落： （1）频率选择性衰落
（2）时间选择性衰落
X 第12页，共47页。
1.1.2 无线电波的传播特性
第 12
页
4、电离层的结构及其对短波信道的影响
由于受到周围建筑物以及地面的反射和散射作用， 往往使同一波源发出的信号沿多条不同的传输路径， 以不同的时间到达接收机。这些经不同路径到达的波， 称为多径波。由于不同路径的信号的传播距离及传播时延
不同，到达接收机时的相位也就不同，从而使接收到的信 号的幅度有时因同相叠加而增强，有时又因反相叠加而减 弱。这样，接收信号的幅度就会产生剧烈的变化，造成畸
X 第3页，共47页。
1.1.1 无线电波段的划分
第 3
页
本书讨论的无线通信覆盖的无线电波频率范围
主要是HF、VHF、UHF和SHF波段。
X 第4页，共47页。
1.1.1 无线电波段的划分
第 4
页
分米波段 ，特高频（UHF），波长为1m-10cm
微 波 厘米波段，超高频（SHF），波长为10-1cm 频 段
1.3.1 基本概念
第 32
页
3、基带传输与频带传输
基带信号：由信源直接生成的信号。
频带信号：基带信号经调制后生成的信号。
在数字通信系统中，在传输距离不太远的情况下，将来自
信息源的数字基带信号直接传输，称为数字基带传输。
将数字基带信号经过载波调制，把频谱搬移到高频 处再传输，这种传输称为数字频带传输。
路径衰耗与距离的n次方成比例，其中n称为路径衰 耗指数，不同传输环境取不同的值。
无线通信基础(双语)教学
Node 3
Node 2 Node 1
Shared Multiple Access Channel
Node 4 Node N
Each node is attached to a transmitter/receiver which communicates via a channel shared by other nodes
Solving multiple access issues Different types:
Channel Partitioning (FDMA TDMA CDMA) Taking Turns (Taking Ring) Random Access (Aloha CSMA)
Orthogonality can be mechanized using a. Space division multiple access (SDMA) b. Frequency division multiple access（FDMA） c. Time division multiple access（TDMA） d. Code division multiple access（CDMA）
A borrowing option may be considered, if all of a cell’s own channels are already occupied and the neighboring cell has spare channels.
In DCA, voice channels are not allocated to different cells on a permanent basis.
Fixed Channel Assignment (FCA) Dynamic Channel Assignment (DCA)
无线通信原理双语lecture.ppt
Wireless LAN Standards:Wi-Fi 802.11b, 802.11a, 802.11g
2019/12/18
16
WLAN Infrastructure
•Network between devices in home and office environment; •Typically gives access to a fixed infrastructure
• Cognitive and Software Defined Radio,
IEEE 802.22(proposed), et al
Area, …
The output of Wireless System Modeling and Design: International standard (IP): 802.11,802.16,GSM…
2019/12/18
17
1.5 WPANs and WMANs
WPANs: Wireless Personal Area Networks
3G Offers enhancements to current applications including greater data speeds, increased capacity for voice and data and a broader range of services.
In 2000, ITU approved the following three standards:
• Wireless Sensor Networks • 3G and beyond • 3.9G (LTE), 4G,et al
Coverage (range)
Wireless Key techniques
2019/12/18
16
WLAN Infrastructure
•Network between devices in home and office environment; •Typically gives access to a fixed infrastructure
• Cognitive and Software Defined Radio,
IEEE 802.22(proposed), et al
Area, …
The output of Wireless System Modeling and Design: International standard (IP): 802.11,802.16,GSM…
2019/12/18
17
1.5 WPANs and WMANs
WPANs: Wireless Personal Area Networks
3G Offers enhancements to current applications including greater data speeds, increased capacity for voice and data and a broader range of services.
In 2000, ITU approved the following three standards:
• Wireless Sensor Networks • 3G and beyond • 3.9G (LTE), 4G,et al
Coverage (range)
Wireless Key techniques
无线通信基础(双语)_教学课件_11
2 Es x(t ) cos2f c t n Ts Es cos n 2 2 cos2f c t Es sin n sin 2f c t Ts Ts
1 t nTs
2 t nTs
Where 1 t nTs and 2 t nTs form the orthonormal set which defines the signal space for the modulation
3.3.2 Coherent Reception in a Flat Slow Rayleigh Fading Channel
BPSK QPSK
MSK
Consider coherent BPSK reception over an AWGN channel:
AWGN channel
xt
I n I n 1 cos n Qn 1 sin n 0, 1, 1 2 Qn I n 1 sin n Qn 1 cos n 0, 1, 1 2
In general, the baseband in-phase and quadrature components can be represented in terms of the carrier phase of a π/4-DQPSK signal for the symbol by
To combat the effect of the phase distortion on signal detection, π/4-DQPSK is π/4 shift QPSK combined with differential encoding. Information is carried by the phase difference of the adjacent transmitted symbols. If the phase distortion introduced by a wireless channel does not change much over an internal of two symbol duration (which is normally true), the phase difference between two adjacent symbols is almost independent of the channel phase distortion
1 t nTs
2 t nTs
Where 1 t nTs and 2 t nTs form the orthonormal set which defines the signal space for the modulation
3.3.2 Coherent Reception in a Flat Slow Rayleigh Fading Channel
BPSK QPSK
MSK
Consider coherent BPSK reception over an AWGN channel:
AWGN channel
xt
I n I n 1 cos n Qn 1 sin n 0, 1, 1 2 Qn I n 1 sin n Qn 1 cos n 0, 1, 1 2
In general, the baseband in-phase and quadrature components can be represented in terms of the carrier phase of a π/4-DQPSK signal for the symbol by
To combat the effect of the phase distortion on signal detection, π/4-DQPSK is π/4 shift QPSK combined with differential encoding. Information is carried by the phase difference of the adjacent transmitted symbols. If the phase distortion introduced by a wireless channel does not change much over an internal of two symbol duration (which is normally true), the phase difference between two adjacent symbols is almost independent of the channel phase distortion
无线通信基础(双语)_教学课件_16
Collision
2
3 Time
Collision mechanism in slotted ALOHA
Let S be the throughput, defined as the successfully
transmitted traffic load, and G be the total offered
Orthogonality between two signals
Conflict-Free Mulitiple Access
Random Access and Variants
BS
MS MS MS
MS
MS
The transmission in the downlink can be heard by each and every user in the cell, this mode of transmission is referred to as broadcasting The transmission in the uplink to the base station is many-to-one, and is referred as multiple accss
Aloha
CSMA
In certain situations, it may be advantageous to
employ a non-conflict-free multiple access scheme. In conflict-free multiple access system, random access is often used to gain the initial access to the syand
2
3 Time
Collision mechanism in slotted ALOHA
Let S be the throughput, defined as the successfully
transmitted traffic load, and G be the total offered
Orthogonality between two signals
Conflict-Free Mulitiple Access
Random Access and Variants
BS
MS MS MS
MS
MS
The transmission in the downlink can be heard by each and every user in the cell, this mode of transmission is referred to as broadcasting The transmission in the uplink to the base station is many-to-one, and is referred as multiple accss
Aloha
CSMA
In certain situations, it may be advantageous to
employ a non-conflict-free multiple access scheme. In conflict-free multiple access system, random access is often used to gain the initial access to the syand
无线通信基础(双语)_教学课件_15
7 7 6 1 5 4 6 1 1 5 4 1 1 3 3 7 2 1 2 5 4 6 1 3 2
Interference from other mobiles at the cellsite receiver in the same cell is intracell interference, interference from other cells is intercell interference.
q 6 100 4.9492
14
N q 3 8.165 9
2
If we use a better approximation of the distance between the mobile and the first interfering base station as illustrated in figure, then the S/I ratio can be expressed as:
To formulate the probability of call blocking, consider a radio cell which has been allocated J channels, and assume that The aggregate arrival traffic is Poisson distributed with rate ; The channel holding time is exponentially distributed with parameter . That is, the mean channel holding time of the call is 1, correspond ing to a mean service rate of for the call.
无线通信基础(双语)_教学课件_14
Capacity Expansion by Frequency Reuse
Cellular Layout for Frequency Reuse
Geometry of Hexagonal Cells
Frequency Reuse Ratio
The capacity of the cellular system is defined by the total number of channels available, and the total number of channels available in a cellular system is finite The system capacity as a function of the total number available channels depends on how the available channels are deployed Cells which use the same set of frequencies are referred to as cochannel cells, and the interference between cochannel cells is referred to as cochannel interference.
3. Cellular layouts
Cellular layouts and performance studies are based on regular topologies, and all our discussions will be based on a hexagonal topology
2. Location management
无线通信基础(双语)_教学课件_10
In M-ary signaling, the mth waveform is represented as
2 Es 2 (m 1) xm (t ) cos 2 f ct 0 Ts M
0 t Ts , m 1, 2,..., M
where 0 0或 M ; or 式中:
yn (Ts ) r hn (Ts )d
r n ( )d
Ts
r n ( )d
0
rn
Given the demodulator output r
, the decision device is to perform a mapping from r to an estimate s of the transmitted symbol in a way ˆ that will minimize the probability of error in the decision making process.
Ts 0
n 1, 2, , N
r (t )
1 (t )
dt
Ts 0
r1 r2
2 (t )
N (t )
dt
Ts 0
r
dt
Ts 0
rN
r (t )
h1 t
t Ts t Ts t Ts
r1 r2
h2 t
r
hN t
rN
hn (t ) n (Ts t )
2 Eb x1 (t ) cos( 2f ct ), Tb 2 Eb x2 (t ) cos( 2f ct ), Tb
Only the basis function, 1 (t ) represent the BPSK signals.
无线通信基础(双语)_教学课件_17
Spectral Efficiency of Wideband TDMA (ηW-TDMA)
ቤተ መጻሕፍቲ ባይዱ
Assuming
τp ---- the time duration for the preamble τt ---- the time duration for the trailer
Tf ---- the frame duration
The cell capacity is defined as the maximum number of mobile users that can be supported simultaneously in each cell. With TDMA, the maximum number of simultaneous users that can be accommodated during one use of the available frequency spectrum is
Cell area in km2
Frequency reuse factor
Multiple access scheme used
The spectral efficiency of a mobile communication system can be represented as a combination of two independent components : One component that depends on the system parameters
N u Bc 1 Bs The spectral efficiency of narrowband TDMA is then given by
无线通信基础(双语)_教学课件_3
What does “dB” mean?
dB can express ratios, but what about absolute quantities? Similar units reference an absolute quantity against a defined reference. [n mW]dBm = [n/mW]dB [n W]dBW = [n/W]dB
What does “dB” mean?
Ex: Attenuation from transmitter to receiver PT=100, PR=10 attenuation is ratio of PT to PR [PT/PR]dB = 10 log(PT/PR) = 10 log(10) = 10 dB Useful numbers: [1/2]dB -3 dB [1/1000]dB = -30 dB
Effective area of an isotropic antenna
However, from electromagnetic theory, we note that the effective area of an isotropic antenna in any direction is given by: A= 2 / (4 )
2. Effective area of an isotropic antenna
The power received by an antenna of effective area A is given by:
PR=S· A
However, from electromagnetic theory, we note that the effective area of an isotropic antenna in any direction is given by: A= 2 / (4 ) Thus PR=S· t 2 / (4 d) 2 A=P
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Okumura Model Okumura-Hata Path Loss Model COST 231 Model Lee’s Path Loss Model
Empirical formulation to match Okumura model
Suitable for large cell
ro = 1mil = 1,6 km
Pr
r
Po
k
n
Pr
Po.
d do
.
f fc
.o
Pr
Po
10k
log
d do
10n log
PL,urban (d )dB 46.3 33.9 log10( fc ) 13.82 log10(ht ) a(hr ) (44.9 6.55 log10(ht )) log10(d ) CM
Where a(hr) is the same correction factor as before and CM is 0 dB for medium sized cities and suburbs and 3dB for metropolitan areas.
The path loss is represented as a function of
The carrier frequency, [150, 1500]MHz Antenna heights of base station and mobile
station, hb[30, 200]m, hm[1, 10]m The distance between the base station and
station, hb[30, 200]m, hm[1, 10]m The distance between the base station and
mobile station, [1, 20]Km
Lee’s model can be used to predict area-to-area path loss. The model consists of two parts:
The COST 231 model is restricted to the following range of parameters:
The carrier frequency, [1.5, 2]GHz Antenna heights of base station and mobile
where
A 69.55 26.16 log( fc ) 13.82 log(hb ) a(hm ) B 44.9 6.55log(hb )
C 5.4 2log( fc 28)2 D 40.94 4.78log( fc )2 18.33log( fc )
Lp (d ) Lp (d ) dB
Lp
(d0
)
10
log
d d0
dB ,
d
d0
Without shadowing With shadowing
PL(d )dB L( fc , d ) Aμ ( fc , d ) G(ht ) G(hr ) GAREA
mobile station, [1, 20]Km
The path loss in dB is given by
Lp
dቤተ መጻሕፍቲ ባይዱ
A B log10d A B log10d
C
A
B
log10
d
D
for urban area for suburban area for open area
For a large city
ahm 38.2.2[l9o[glo1g011011.7.554hhmm]]2241..917
for fc 200MHz for fc 400MHz
fc=900MHz hb=50m hm=3m
The Hata model was extended by the European cooperative for scientific and technical research (EURO-COST) to 2GHz
a(hm) is the correction factor for mobile antenna height, and is given by
For a small and medium city
ahm [1.1log10 fc 0.7]hm [1.56log10 fc 0.8]
The power at a 1.6km (1 mile) of interception P0 in dBm The path-loss exponent k.
The specified set of conditions is as follows:
Carry frequency fc = 900MHz Base station antenna height = 30.48 m(100 ft) Base station power at the antenna = 10 W Base station antenna gain = 6 dB above dipole gain Mobile station antenna height = 3 m (10 ft) Mobile station antenna gain = 0 dB above dipole gain
Path loss prediction for a specified set of conditions Adjustment factors for a set of conditions different from the specified one
The model requires two parameters: