MSIT 413: Wireless Technologies - Northwestern University

N O R T H W E S T E R NU N I V E R S I T Y

MSIT | Master of Science in Information Technology

MSIT 413: Wireless Technologies Week 2

Michael L. Honig Department of EECS

Northwestern University

September 2017 1



Wireless Standards: Our Focus

Cellular PAN MAN LAN Sensor/IoT GSM CDMA2000 WCDMA UMTS 1xEVDO 1xEVDV 1G/2G/3G LTE (4G) 3GPP/3GPP2 5G

WiFi 802.11a/ac/b/g/n

802.16 WiMax

Bluetooth ZigBee Z-Wave NFC Sigfox Neul LoRaWAN

2



Classification of Wireless Systems

•  Cellular •  Wireless Local Area Networks (WLANs) •  Wireless Metropolitan Area Networks

(WMANs) •  Wireless Personal Area Networks (WPANs) •  Sensor Networks

3



Comparison of Wireless Systems

4



Wireless Local Area Networks (WLANs)

•  Very high data rates (up to 600 Mbps/user!)

•  Low mobility within confined region (building or campus)

•  Unlicensed bands –  Industrial, Scientific, Medical (ISM): 2.4 GHz –  National Information Infrastructure (UNII): 5 GHz

•  Must accept interference, therefore uses spread spectrum signaling, or random access with collision avoidance.

•  Family of standards (IEEE 802.11)

5



Overview of 802.11 Standard

IEEE 802.11

IEEE 802.11b Extension

2 Mbps DQPSK

1 Mbps DBPSK

1 Mbps 2GFSK

2 Mbps 4GFSK

Diffuse IR DS-SS FHSS

850 to 950 nm 2.4 GHz

6

11 Mbps DQPSK-CCK

5.5 Mbps DQPSK-CCK



7

Overview of 802.11 Standard

IEEE 802.11

11 Mbps DQPSK-CCK

5.5 Mbps DQPSK-CCK

IEEE 802.11b Extension

2 Mbps DQPSK

1 Mbps DBPSK

1 Mbps 2GFSK

2 Mbps 4GFSK

Diffuse IR DS-SS FHSS

850 to 950 nm 2.4 GHz

discontinued

discontinued



WLAN Family of Standards: 802.11 •  802.11:

2 Mbps (with fallback to 1 Mbps), 1997 & 1999

•  802.11b: provides additional 5.5 and 11 Mbps rates in the 2.4 GHz band

•  802.11a: provides up to 54 Mbps in the 5 GHz band

•  802.11g: Supports roaming, higher rate, backward compatible with 802.11b

•  802.11n: High throughput amendment using multiple antennas (Multi-Input Multi-Output (MIMO))

•  802.11ac: High throughput in 5 GHz band (> 1 Gbps) using wider bandwidth, multi-user MIMO 8



Additional 802.11 Standards •  802.11ad (WiGig): up to 7 Gbps in 60 GHz band (2016) •  802.11ax: enhancement of 11ac, introduces OFDMA, scheduling •  802.11e: QoS & Security Enhancements •  802.11f: Inter Access Point Protocol (IAPP) •  802.11h: Power Management for 5 GHz in Europe •  802.11i: Security enhancements •  802.11j: Enhancements to 802.11a for operation in Japan •  802.11k: Radio resource management •  802.11m: Technical corrections and clarifications •  802.11u: Interfacing with external networks •  802.11v: Upper layer interface for managing 802.11 equipment

9



802.11a/b/g/n Comparison

Comparison table

10



Integrated WLAN-Cellular Network

MS

cellular! WISP/Operator Hotspot!

BTS"

As the user moves, different access choices become available.!

Internet!

BSC

AP"AP"AP"

Home! Enterprise!

Ethernet"segments"

AP"

Application Servers!



802.11 Extension to Cellular

Handoff to 802.11

Cellular (LTE) connection

12



Integrated WLAN/Cellular Network

•  High data rates at hot spots covered by WLANs. •  Lower data rates elsewhere provided by cellular. •  Single account; single bill •  Roaming, session mobility •  Common applications and services •  Cellular traffic à WiFi offload

13



Classification of Wireless Systems

•  Cellular •  Wireless Local Area Networks (WLANs) •  Wireless Metropolitan Area Networks

(WMANs) •  Wireless Personal Area Networks (WPANs) •  Sensor Networks

14



Personal Area Networks (PANs)

15



Bluetooth: A Global Specification for Wireless Connectivity

•  Wireless Personal Area Network (WPAN).

•  Provides wireless voice and data over short-range radio links via low-cost, low-power radios (“wireless” cable).

•  Initiated by a consortium of companies (IBM, Ericsson, Nokia, Intel)

•  IEEE standard: 802.15.1 16



Bluetooth Specifications

•  Allows small portable devices to communicate together in an ad-hoc “piconet” (up to eight connected devices).

•  Frequency-hopped spread-spectrum in the 2.4 GHz UNII band.

•  Range set at 10m.

•  Gross data rate of 1 Mbps (TDD). –  64 kbps voice channels

•  Interferes with 802.11b/g/n

•  Second generation (Bluetooth 3.0+) supports rates up to 25 Mbps. Competes with Wireless USB.

17



Wireless Challenges

18



Today

•  Cellular terminology •  Interference and capacity (voice) •  Performance measures (SINR, user capacity) •  Blocking and grade of service •  Channel assignments

19



Cellular Concept

Cellular Switch (MTSO)

Handoff

Enables frequency reuse!

PSTN

Low power Transmitters

Location Database

Micro- cells

20



Cellular Frequency Assignments

E D

F

C A

E B

G D

C

E

A B

C

D F

A G

B A

G D

C

B A

F G

C G D

A D

B C

F E

G

B

cell cluster (contains all channels) co-channel cells

21



Example of Cellular Layout

drive test plots Opensignal.com

22



Cellular Model •  Hexagonal cells •  Regular spacing •  Frequency reuse limited by co-channel interference. •  Received power decreases with distance.

Note: “Freq. i” à group of channels (f1,f2, , fK) Actual cell “footprint” will be irregular (depends on terrain, etc.)

…

23



Cellular Terminology

•  Cell cluster: group of N neighboring cells which use the complete set of available frequencies.

•  Cell cluster size: N

•  Frequency reuse factor: 1/N

•  Uplink or reverse link: Mobiles à Base station

•  Downlink or forward link: Base station à mobiles

•  Co-channel cells: cells which are assigned the same frequencies

C

D F

A

B A

F G

C G D

A D

B C

F E

G

B

cell cluster

24



Frequency Reuse (Ex) •  Given

–  50 MHz for Frequency Division Duplex (FDD) cellular

–  200 kHz simplex channel (one direction) –  Cell cluster size N=3

•  Channel Bandwidth (BW) = •  Total available channels = •  Available channels per cell =

25



Frequency Reuse (Ex) •  Given

–  50 MHz for Frequency Division Duplex (FDD) cellular

–  200 kHz simplex channel (one direction) –  Cell cluster size N=3

•  Channel Bandwidth (BW) = 2 x 200 = 400 kHz •  Total available channels = 50,000/400 = 125 •  Available channels per cell = 125/3 ≈ 41

26



Co-Channel Cells

A

A A

A

A

A

A

i=3, j=2 N=i2+ij+j2=19

For hexagonal model, N is restricted: N=i2+ij+j2, where i, j are positive integers

Other examples: i= j=1 è N=3 i=0, j=2 è N=4 i=1, j=2 è N=7 i=2, j=2 è N=12

27



Example with i=j=1 (N=3)

C A

C A

B A

C B

B A

C

C B

C A

B B A

A C

A C

B A

C

B

cell cluster

Cell cluster shape also covers the plane. 28



Interference and Capacity •  As N increases:

–  Interference –  Channels per cell –  Capacity

•  As N decreases: –  Interference –  Channels per cell –  Capacity

29



Interference and Capacity •  As N increases:

–  Interference decreases –  Channels per cell decrease –  Capacity decreases

•  As N decreases: –  Interference increases –  Channels per cell increase –  Capacity increases

Objective: choose the minimum N subject to acceptable interference levels. 30



Sources of Interference

31



Sources of Interference •  Other users – Multiple-Access interference •  Multipath (reflections of signals) •  Other devices or systems (e.g., in unlicensed band)

•  Categories: –  Co-channel (frequency bands coincide) –  Adjacent-channel

frequency Channel 1 Channel 2

power Note: as transmitted power increases, so does the interference

32



802.11b/g/n Channels (2.4 GHz)

•  14 overlapping (staggered) channels (11 in the U.S.) •  Center frequencies are separated by 5 MHz •  Bandwidth/interference controlled by “spectral mask”

–  30 dB attenuation 11 MHz from center frequency –  50 dB attenuation 22 MHz from center frequency

Channels: 1 6 11

Comparison table

33

frequency à



Co-Channel Reuse Ratio

1 2

5 4

3 . R

1 2

5 4

7 6

3 .

D

7 6

NRD 3=

From hexagonal geometry

As D/R increases, interference decreases (improved isolation between co-channel cells). 34



Co-Channel Reuse Ratio •  Small D/R:

–  Small N, large number of channels/cell –  More interference (fixed cell size)

•  Large D/R: –  Small capacity –  Less interference (improved call quality)

•  Numerical examples: i=1, j=0 è N=1, D/R= √3 i= j =1 è N=3, D/R= 3 i=1, j=2 è N=7, D/R= 4.58 i=2, j=2 è N=12, D/R= 6

35



Performance Measure: Signal-to-Interference-Plus-Noise Ratio (SINR)

•  Expressed in dB (10 log (SINR))

•  Typically, the interference power dominates (ignore noise) –  SINR à Signal-to-Interference Ratio (SIR or S/I)

•  Total interference power is the sum over all interferers:

–  More co-channel users à more interference

Power Noise Power ceInterferenPower Signal Received

+=SINR

36



Why is SINR Important?

37



Why is SINR Important? •  The data rate depends on SINR:

•  Recall the Shannon rate: R = B log2 (1 + SINR) –  B is bandwidth (Hz), rate is measured in bits per second –  Is it better to increase bandwidth or power?

•  Why is SINR important for a voice service?

SINR (dB)

Data rate (bits/sec)

actual curve depends on technology.

38



Why is SINR Important?

•  For a voice service, R is fixed (say, around 10 kbps). This determines a minimum SINR that is required:

SINR

Data rate

voice rate

required SINR

•  Smaller SINR à more co-channel users can be served •  Required SINR for voice users in cellular systems:

–  1G (AMPs): SINR ≥ 18 dB ≈ 63.1 –  2G (GSM): SINR ≥ 12 dB ≈ 16 –  2G (CDMA): SINR ≥ 7 dB ≈ 5 –  3G (CDMA): SINR ≥ 3-5 dB ≈ 2-3 39



First Tier Interference: Uplink

Mobile-to-Cell Site Interference (Uplink)

6 co-channel cells (due to hexagonal cells) à 6 times the interference from a single cell

40



First Tier Interference: Downlink

Cell Site-to-Mobile Interference (Downlink)

6 co-channel cells (due to hexagonal cells) à 6 times the interference from a single cell

41



Signal Attenuation

reference distance d0

distance d

Reference power at reference distance d0 Path loss exponent

In dB: Pr = P0 (dB) – 10 n log (d/d0)

Pr (dB)

log (d)

slope = -10n, n ~ 2 to 4 for urban cellular

P0

log (d0)



First Tier Co-Channel Cells

1 R

D First Tier

Interfering Cell

Signal power S ≈ P0 (R/d0)-n Total Interference power

I ≈ 6 P0 (D/d0)-n Therefore S/I = R-n/(6D-n) = (D/R)n/6 S/I (dB) = 10n log (D/R) – 10 log 6 = 10n log (3N)1/2 – 10 log 6 (will take n=4)

43



D

Same Principle for Other Wireless Devices

Interfering router

Signal power S ≈ P0 (R/d0)-n Total Interference power

I ≈ 3 P0 (D/d0)-n Therefore S/I = R-n/(6D-n) = (D/R)n/3 S/I (dB) = 10n log (D/R) – 10 log 3 = 10 n log (3N)1/2 – 10 log 3 (will take n=4)

R

44



SIR vs. Frequency Reuse

S/I (dB) = 40 log (3N)1/2 – 10 log 6

Cell cluster size N

Sig

nal-t

o-In

terfe

renc

e R

atio

(dB

)

45



S/I Example

•  Suppose desired S/I = 10 dB = 10

•  From the graph, we can take N=3, that is, we need a 3-cell reuse pattern.

•  But is this really adequate?

46



Worst Case Interference

R

D D+R

D+R

D-R

D-R

D

D

Recalculating the S/I taking into account the different distances between co-channel cells would give an S/I < 10 dB. To make sure the S/I ≥ 10 dB, we must increase N à 4 (i=0, j=2), for which the S/I = 14 dB. However, even 14 dB may not allow for additional Impairments due to different terrains, imperfect cell site location. Hence taking N=7 is safer… Drawback?

47



Worst Case Interference

R

D D+R

D+R

D-R

D-R

D

D

Recalculating the S/I taking into account the different distances between co-channel cells would give an S/I < 10 dB. To make sure the S/I ≥ 10 dB, we must increase N à 4 (i=0, j=2), for which the S/I = 14 dB. However, even 14 dB may not allow for additional Impairments due to different terrains, imperfect cell site location. Hence taking N=7 is safer… Changing N=3 à N=7 reduces the capacity by a factor of 3/7!

48



To Increase Capacity in Cellular Systems:

49




•  Buy more spectrum •  Antenna sectoring •  Cell splitting •  Different cell configurations (zone microcell) •  Power control •  Migrate to higher efficiency systems

1G à 2G à 3G à 4G (LTE)

50




•  Assign more spectrum •  Antenna sectoring •  Cell splitting •  Different cell configurations (zone microcell) •  Power control •  Migrate to higher efficiency systems

1G à 2G à 3G à 4G (WiMAX or LTE)

51



Sectorization (120o)

120o

52

120o

120o

Channels are divided into 3 groups, assigned to the different sectors.

Channels 1, 4, 7

Channels 2, 5, 8

Channels 3, 6, 9



Sectorization (120o)

120o

Two Interferers in First Ring per Sector

Cell Site-to-Mobile Interference (Downlink) Mobile-to-Cell Site Interfaces (Uplink)

120o

120o

Use directional antennas to reduce the number of interferers from 6 to 2. S/I increases by factor of 3 (about 5 dB)

53



60o Sectorization One Interferer in First Tier per Sector

Cell Site-to-Mobile Interference (Downlink) Mobile-to-Cell Site Interfaces (Uplink)

60o 60o

60o

60o

60o 60o

Number of interferers reduced from 6 to 1. S/I increases by factor of 6 (about 8 dB).

54



R D + 0.7 R

60o Sectorization: Worst Case Interference

. .

M

.

. D

2

1

Even larger improvement relative to worst-case omni-directional antennas (about 11 dB).

55



Disadvantages of Sectoring

56



Disadvantages of Sectoring

•  Additional complexity •  Increased handoffs

(can be accommodated at base station instead of cellular switch (MTSO), so not a major concern)

•  Less effective in dense urban environments due to scattering of radio waves across sectors.

•  Reduced trunking efficiency

57



“Smart” Antennas (Beamforming)

Different beams can use the same frequency!

Narrow “beam” focused on one user

This is one type of Multi-Input Multi-Output (MIMO) technology. 58






59



Cell Splitting

4 7

1

2 1

3 6

5

3

Growing by Splitting Cell 4 Into Cells of Small Size

7

1

2

1

3 6

5

3

(4) (2)

(3) (6)

(7) (5)

(1)

Smaller cells è lower power, more channels available per unit area. 60



Mixed Micro/Macro Cells How to accommodate both pedestrian (low-mobility) and high-mobility users?

Micro-cell overlay reduces capacity of macro-cellular network!

High power (expensive) Transmitters

Micro-cell (e.g., city block)

Low power (inexpensive) transmitters

Macro-cell (1-2 mile radius)

61



“Umbrella” Cell

High mobility users communicate with large (high power base station). Must support handoff between macro- and micro-cells. (Mobile speed must be estimated at base station.)

62



802.11 Extension to Cellular

Handoff to 802.11

Cellular connection

63






64



Zone Microcells

x

xR

T

x

xR

T

Base Station

x

xR

T

Zone

Sel

ecto

r Microwave or fiber optic link

•  Any channel can be assigned to any zone. •  No handoff between zones. •  Radiation localized, improves S/I. •  Highways, urban corridors.

65

“Remote Radio Heads”



Cellular Hierarchy

66



Remote Antennas / Radio Heads

67

Blue circles represent remote antennas or “radio heads”. Signals from a cluster of antennas are processed by a “Remote Central Processor”. Envisioned as part of 5G.





2G à 3G à 4G (LTE) à 5G?

68



Power Control and System Migration

•  Power control –  Advantages?

69



Power Control and System Migration •  Power control

–  Minimizes interference –  Saves battery power –  Solves “near-far” problem (crucial in CDMA)

70



Power Control and System Migration •  Power control

–  Minimizes interference –  Saves battery power –  Solves “near-far” problem (crucial in CDMA)

•  Migration to 3G/4G/802.11 extensions… –  Target S/I decreases;

enables increased frequency reuse •  IS-136 (2G) requires S/I > 12 dB à N=4 •  GSM (2G) requires S/I > 9 dB à N=3 •  IS-95 requires S/I > 7 dB (N=1) •  CDMA 2000 requires S/I > 3-5 dB (depending on mobility)

71



Will 4G Satisfy Projected Demand?

72



Increases in Cellular Capacity Capacity(SpectralEffi

ciency

73



Trunking and Grade of Service (GoS) Idea (trunking): Allocate channels on a per-call basis.

Select from pool of available channels.

74



Trunking and Grade of Service (GoS) Idea (trunking): Allocate channels on a per-call basis.

Select from pool of available channels.

time

System capacity

Number of Calls in progress

1

2

3

4

blocked or delayed call

service times

Example: set of channels is (f1, f2, f3)

f2 f3 f2 f2 f1 f1 call arrival f1

75



Grade of Service (GoS)

•  GoS measures: –  Blocking probability –  Probability that delay > time T

(e.g., maximum acceptable delay for voice call)

•  GoS pertains to busiest hour (e.g., rush hour)

•  GoS depends on: –  ??

76



Grade of Service (GoS)

•  GoS measures: –  Blocking probability –  Probability that delay > time T

(e.g., maximum acceptable delay for voice call)

•  GoS pertains to busiest hour (e.g., rush hour)

•  GoS depends on: –  Number of channels –  Call arrival rate λ–  Average holding time H

Traffic engineering problem: determine the number of channels so that GoS meets some target performance (e.g., Prob of blocking < 2%). 77



Traffic Intensity Traffic intensity is defined as λ H, and measured in Erlangs.

Example: λ=1 call/minute, H= 1 minute, λ H = 1 Erlang è on average, users request 1 channel λ H = ½ Erlang è there are no requests for channels more than

50% of the time

f1

f2

fC

Offered traffic (“load”) λ H = A Channel

assignment

Offered traffic is not the same as the carried traffic, due to blocking!

Departing, or “carried” traffic

C channels . . .

78



Erlang B Formula (1917) •  Formula for computing blocking probability assuming:

–  Blocked calls disappear –  Requests for channel arrive according to a Poisson random

process (inter-arrival times are independent, exponentially distributed)

•  Applies to infinite user population

–  C channels available –  Exponentially distributed

service time –  Blocking probability formula:

time

Prob(call lasts < t secs) 1

3 minutes

1-e-t/τ

“Blocked calls cleared” formula (A = λH) 79



Erlang B Curves

80



Erlang C Formula

•  Blocked calls enter a queue •  First come, first served •  Call is blocked if queuing delay D > T •  Formula for probability of blocking given in text.

81



Example

•  Take PB = 2%, C=5 è Offered load A < 1.7 Erlangs

•  If each user is busy 1/10 of the time (0.1 Erlang/user), Total # users < 17 (maximum)

•  For C=10: A < 5 Erlangs or 50 users

•  For C=100: A=88 or 880 users

•  Observation: A/C (or users per channel) increases with C (e.g., 10 groups of 10 channels can support only 500 users)

•  Trunking efficiency increases as C increases

82



Trunking Efficiency

•  Refers to the traffic intensity (Erlangs) that can be supported given a fixed number of channels and a target blocking probability.

•  For a fixed blocking probability: –  Trunking efficiency improves with the number of channels.

è Best to pool as many channels as possible.

83



Voice Capacity •  Defined as

–  Example: SE = 2 Erlangs/MHz/km2

è 1 MHz supports 2 Erlangs/km2 (Note that 1 km2 may correspond to a cell.)

–  If on average, each user is active 1/10 of the time, then 1 Erlang corresponds to 10 users.

•  Traffic per cell depends on…

)(kmarea Total(MHz)] bandwidth [Total(Erlangs) carried trafficTotal

2×

84



•  Defined as

–  Example: SE = 2 Erlangs/MHz/km2 è 1 MHz supports 2 Erlangs/km2 (Note that 1 km2 may correspond to a cell.)

–  If on average, each user is active 1/10 of the time, then 1 Erlang corresponds to 10 users.

•  Traffic per cell depends on: –  Number of channels –  Grade of Service (e.g., typically 2%) –  S/I requirement (determined by cluster size N)

)(kmarea Total(MHz)] bandwidth [Total(Erlangs) carried trafficTotal

2×

85

Voice Capacity



Effect of Sectorization

•  Does sectorization increase user capacity (Erlangs) per cell?

86



Effect of Sectorization

•  For fixed N, sectorization –  Increases the S/I –  Reduces trunking efficiency

•  Example: 90 channels per cell, 120o sectors gives 30 channels per sector, which reduces the number of Erlangs that can be supported for a given blocking probability.

•  Can we use sectorization to increase user capacity? –  Yes, must also reduce N

•  Increases channels per cell è increases user capacity •  Increases interference, lowers S/I •  Sectorization then increases S/I

87



Channel Allocation

•  Consider GSM: 25 MHz (simplex), 200 kHz channels à 125 channels (1 is used for control signaling)

•  How to allocate channels to cells?

Suburb (lightly loaded)

Train station

Shopping mall

88



Channel Allocation


•  How to allocate channels to cells? –  Objective: equalize blocking probability

(target is around 2%)

•  Fixed channel allocation assigns fixed set of channels to each cell –  Drawback?


Train station

mall

89



Channel Allocation


•  How to allocate channels to cells? –  Objective: equalize blocking probability

(target is around 2%)

•  Fixed channel allocation assigns fixed set of channels to each cell. –  Drawback: traffic is time-varying

•  Dynamic channel allocation varies the number of channels per cell, depending on the load.


Train station

mall

90



Dynamic Channel Allocation

2,6 1,3

Channels already in use

5

1,3,4

new call: search for channel

91



Dynamic Channel Allocation

•  Channels assigned from complete set of available channels

•  Each user searches for a channel with high SINR (low interference)

•  No frequency planning!

2,6 1,3

Channels already in use

5

1,3,4

new call: search for channel

4

92



802.11b/g/n Channels

•  14 overlapping (staggered) channels (11 in the U.S.) •  Center frequencies are separated by 5 MHz •  Bandwidth/interference controlled by “spectral mask”

–  30 dB attenuation 11 MHz from center frequency –  50 dB attenuation 22 MHz from center frequency

Channels: 1 6 11

Comparison table

93



Dynamic Channel Allocation: 802.11b/g

Channel 6 Channel 1 Channel 11

94




Channel 6 Channel 1 Channel 11

Channel 6

Add new router

interference

95




Switches to channel 1 Channel 1 Channel 11

Channel 6

interference

96




channel 1 Switches to channel 6 Channel 11

Channel 6

interference

97




channel 1 channel 6 Channel 11

Switches to channel 1

interference

Dynamic channel assignment becomes unstable! 98



Overlapping Channel Assignment

channel 1 channel 6 Channel 11

Channel 3

Interference (less than before) Interference

(less than before) power

frequency Channels: 1 3 6 99



Channel Allocation •  Objective: equalize grade of service (blocking probability) over coverage area

à Allows increase in subscriber pool.

•  Fixed Channel Assignment (FCA): channels assigned to each cell are predetermined.

–  Separate channels within a cell to avoid adjacent-channel interference –  Nonuniform FCA: distribute channels among cells to match averaged traffic load

over time.

•  Channel borrowing: borrow channels from neighboring cell –  Temporary: high-traffic cells return borrowed channels –  Static: channels are non-uniformly distributed and changed in a predictive manner to

match anticipated traffic

•  Dynamic Channel Assignment (DCA): channels are assigned to each call from the complete set of available channels

–  Must satisfy S/I constraint –  Channels returned to pool after call is completed –  Can be centralized (supervised by MSC) or distributed (supervised by BS) –  Distributed DCA used in DECT 100



FCA vs. DCA

•  Moderate/High complexity –  Must monitor channel occupancy,

traffic distribution, S/I (centralized)

•  Better under light/moderate traffic

•  Insensitive to changes in traffic

•  Stable grade of service

•  Low probability of outage (call termination)

•  Suitable for micro-cellular systems (e.g., cordless)

•  Moderate/high call setup delay •  No frequency planning •  Assignment can be centralized or

distributed

•  Low complexity

•  Better under heavy traffic •  Sensitive to changes in traffic •  Variable grade of service •  Higher probability of outage

•  Suitable for macro-cellular systems

(e.g., cellular)

•  Low call setup delay •  Requires careful frequency planning •  Centralized assignment

DCA FCA

101

MSIT 413: Wireless Technologies - Northwestern University

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