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第7回講義資料

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Cellular System Concepts
森 川 博 之
東京大学新領域創成科学研究科
[email protected]
2003.5.23
1
History
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J.C. Maxwell (1831-1879),
– “… we have strong reason to conclude that light itself -- including radiant
heat, and other radiations if any -- is an electromagnetic disturbance in the
form of waves propagated through the electromagnetic field according to
electromagnetic laws.”, Dynamical Theory of the Electromagnetic Field,
1864.
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Statement: “Only in a steady state can a magnetic field exist without causing
an electric field and vice versa. When one is changing, it automatically brings
the other into being for as long as the change continues. These mutually
generating fields must be at right angles to each other, and they must both
travel with the same velocity, which is equal to that of light.”
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Implication: “Other forms of electromagnetic waves than light exist, travel at
the same speed as light, but differ from it in terms of frequency and
wavelength.” Verified experimentally by Hertz in 1887.
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1
History
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1895 Marconi transmits a message to his brother over a distance
1897 逓信省電気試験所月島~第5台場(1マイル)通信実験
1901 Marconi receives first trans-Atlantic wireless message
– A long wave (> 1Km) transmission from the coast of England to the coast
of Canada 700 mile transmission range during day, improved to 2000
miles at night.
1903 海軍36式無線電信機(200マイル):
「敵艦見ゆ」日本海海戦
1912 Titanic
– A Marconi set was aboard the ocean liner Titantic
when it went down.Two ships near the Titantic had
shut down their radio sets at 11 PM -- several hours before the disaster.
Marine radio telegraphy become widespread, and is monopolized by
Marconi.
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History
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1908 銚子無線局~洋上船舶局無線電報業務
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1912 TYK式放電ギャップ⇒無線電話
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1920s Marconi discovers that short waves, reflected off
of the Ionosphere, offered a much better communications
method requiring substantially lower power, and more compact antenna
systems and radio sets.
– First time in history that something smaller and cheaper actually
outperformed something larger and more expensive!
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1920s ラジオ放送開始
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1926 NBC founded
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1928 CBS founded
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1933 Land-mobile to police and fire departments begins
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1935 Frequency Modulation (FM) radio invented by Armstrong
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2
History
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1946 Mobile Telephone Service began in St. Louis, MO
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1953 船舶電話(港湾内停泊船舶)
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1957 列車電話(近鉄名古屋~大阪)
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1964 Improved Mobile Telephone Service, Harrisburg, Pa
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1968 ポケットベル
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1978 Cellular trial in Chicago, Ill
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1979 自動車電話(世界初商用サービス)
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1983 First commercial cellular, Chicago, Ill
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1980- Analog cellular systems: MCS(Japan), AMPS(US), TACS(UK),
NMT(Nordic)
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1990- Digital cellular systems: PDC(Japan), IS-94, 95(US), GSM(Europe)
Digital cordless systems: PHS(Japan), PCS(US), DECT,
CT-2(Europe)
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First Wireless Telephony Service
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1946: FCC grants license to Southwestern Bell Telephone in St. Louis,
Missouri
– Used 150 MHz, 250 watt base transmit power, 25 watt mobile
transmit power
– Used frequency modulation
– Push to talk, half duplex
– Different frequencies for transmit and receive
– Used a single transmitter and antenna for about 80 km coverage
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3
IMTS
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1964: Improved Mobile Telephone Service (IMTS) implemented
– Same single high power transmitter covers the city
– Allows for full duplex operation, talk and listen at same time
– Allows for dialing of calls
– Automatic channel selection by mobile transceiver
– Uses marked-idle channel technique
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Early Systems
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Single transmitter and antenna cover entire city
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4
Cellular Systems
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Multiple Low Power Transmitters and Antennas Cover City
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Cellular System Concept
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Replace single high power transmitter covering the entire service area
with lots of low power transmitters (base stations) each covering a
fraction of the service area (cell)
– Mobiles in sufficiently distant base stations may be assigned
identical channel (frequency, time slot, & code)
– System capacity may be increased without adding more spectrum
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Major conceptual breakthrough in spectral congestion & user capacity
– Requires technological changes such as frequency reuse & cochannel interference, channel allocation, and hand-offs
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5
Frequency Reuse
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cluster
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=1, 3, 4, 7, 9, 12, 13, 16, 19…
1
4
7
1
7
N=i2+ij+j2, where i≧j≧0 are integers
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6
5
6
Tesellations of hexagonal cells require
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2
3
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– Not required in CDMA which has
universal frequency reuse
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2
4
6
Used in FDMA & TDMA based systems
1
7
3
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2
Cells idealized as hexagons
– Not appropriate for microcells,
highways etc.
Ideal hexagonal grid (N=7)
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Example
cluster
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1
7
3
2
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全体のチャネル数
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1
4
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33MHzの帯域,上りと下りでそれぞれ
25kHz の帯域を使用する場合,4セル/
7セル/12セル繰返しの場合,何チャネ
ルとることができるか?
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6
5
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3
2
5
– 330MHz/(25kHz x 2)=660 channels
4
6
1
7
3
2
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N=4: 660/4 ≒ 165 channels
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N=7: 660/7 ≒ 95 channels
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N=12: 660/12 ≒ 55 channels
Ideal hexagonal grid (N=7)
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Frequency Reuse
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Ideal hexagonal grid (N=7)
5
7
1
7
– Less system capacity
1
4
6
– Fewer channels per cell
4
6
5
Assuming that the cell size is kept
constant and fixed spectrum per
cluster, more cells per cluster mean:
– Less co-channel interference (cochannel cells farther apart)
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2
3
5
2
4
6
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1
7
3
Goal is to maximize system capacity
subject to interference limitations
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13
Determining Cluster Size N
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C
C
=
N
I
∑Ii
i =1
=
P0R −γ
N
P0 ∑ (D i ) −γ
i =1
=
1
N
D 
∑  Ri 
−γ
i =1
where C is the desired carrier power, Ii is the signal power of the i-th
interferer, R is the radius of hexagon, and Di is the frequency reuse
distance to the i-th interferer.
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When required C/I is 16dB, N=7 is necessary
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Variations of Cell Sizes
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Microcell
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If cell area is reduced while N is kept constant
– more clusters needed to cover the service area
– C/I is unchanged because D/R is unchanged
– system capacity grows quadratically with cell radius scale factor
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Smaller cells need lower RF transmitted power
– longer battery life, smaller mobile end- points
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Smaller cells result in higher cell- boundary crossings (hand- offs)
– more signaling overhead
– performance degradation (more disruption)
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Street Microcell
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ダイナミックチャネル割当
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TDMAシステムの容量増加策の一つ
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電波受信強度等を利用して適応的にチャネルを割り当てる
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9
セルラーシステム
VLR
HLR
Interexchange
Network (IXC)
AUC
EIR
BSC
Local Exchange
Network
MSC
TSC
BTS
MS
BSC
MSC
Transit
Switching
Center
Local Loop
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セルラーシステム
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Mobile Service Switching Center (MSC)
– 所定地域を管轄、呼ルーティング、呼制御
– PSTNやISDNとのインタフェース
Home Location Register (HLR)
– モバイル加入者の管理
– 加入者情報、呼転送/ルーティング情報
Visitor Location Register (VLR)
– 加入者情報の動的な格納、登録処理
Authentication Center (AuC) / Equipment Identity Register (EIR)
– システムセキュリティ
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位置登録
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位置登録エリア ≫ セル
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別の位置登録エリアに移動したときに、端末はネットワークに通知
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移動端末に接続するときは
– HLRにアクセスして位置登録エリアを調べ、
– 当該位置登録エリアにおいて一斉呼出を行い、
– 端末からの応答を受信すると通信チャネルを決定して端末に送信
し、
– 端末は当該通信チャネルにおいて接続、通信を開始する
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位置データベース
090-xxxx-xxxx
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電話番号:
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移動機:
デジタル800MHz
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料金プラン:
プランA
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現在所在地:
東京都文京区
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留守番電話サービス:
契約無
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キャッチホンサービス:
契約無
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iモードサービス:
契約有
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ワールドコールサービス:
契約無
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転送電話サービス:
契約無
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迷惑電話ストップサービス:契約無
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三者通話サービス:
契約無
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セルラーネットワーク
①一般電話からの着信
②移動交換局への接続
③ホームメモリ局に問い
合わせ位置登録エリア
を知る
④当該移動交換局まで接続
⑤一斉呼出
⑥基地局に応答
⑦未使用のチャネルを選択
し接続制御完了
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ハンドオーバ
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端末主導型ハンドオフ: 分散型
– 受信信号強度を用いてハンドオフを決定
– 空きスロットにおいて隣接セルの信号強度を測定
– 端末での測定結果に基づいてネットワークにハンドオフ要求を送
信
– ネットワークでハンドオフ処理開始
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基地局主導ハンドオフ: 集中型
– 端末からの受信電力が弱くなると、隣接セルに当該端末の受信強
度を調べさせる
– 隣接セルの受信強度が良好であればハンドオフ処理開始
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強制切断率 vs 呼損率
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12
ハンドオーバ
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PDCスロット配置
20ms
基地局下り
TB-M3
基地局上り
RM1-B
移動局側
(M1)
TM1-B
TB-M1
RM2-B
L
RB-M1
TB-M2
RM3-B
I
T: 送信
Ti ⇒ Ri: 対応する送受信用スロット
R: 受信
I: アイドル
LM: アンテナ切替ダイバーシチ用レベル測定
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番号方式
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平成11年1月1日午前2時まで
– 030-CD-EFGHJ
– CD: 事業者識別番号,EFGHJ: 加入者番号
– cf: その昔は発着間距離が160km以内のとき030,160km以遠のとき040
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平成11年1月1日午前2時以降
– 0A0-CD-EFGHJ を 090-ACD-EFGHK に変更
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CDコードの一覧
– http://www.soumu.go.jp/joho_tsusin/top/tel_number/number_shitei.html
– 090-999-***** は「Jフォン関西」,090-777-***** は「ドコモ中国」
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Assignment6
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FDMA方式のcellular systemにおいて,上り/下り各方向にそれぞれ
12.5MHzの帯域を使用することができるとする.1チャンネルあたり
の帯域が30kHz,Guard Bandが10kHzであるとすると,利用可能なチャ
ンネル数は全部でいくつか.
締め切り:05/30/2003 (Fri) 24:00
提出方法:[email protected] までメールで送る
と共に,SOIにも提出して下さい
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