HANDOFF, CO-CHANNEL INTERFERENCE and LINK BUDGET...

HANDOFF, CO-CHANNEL INTERFERENCE and

LINK BUDGET PARAMETERS

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Contoh Soal 1

Sebuah sistem seluler TDD mempunyai bandwidth sebesar 10 MHz, besar tiap channelnya adalah 20 kHz, apabila control channel yang dialokasikan untuk sistem tersebut adalah sebesar 1 MHz, hitung alokasi masing-masing voice channel dan control channel untuk tiap selnya untuk ukuran clusternya 3, 4 dan 7 !

Jawaban Soal 1

𝑗𝑢𝑚𝑙𝑎ℎ 𝑐ℎ𝑎𝑛𝑛𝑒𝑙 =10 𝑀𝐻𝑧

20 𝑘𝐻𝑧=

107

20 × 103= 500 𝑐ℎ𝑎𝑛𝑛𝑒𝑙𝑠

𝑎𝑙𝑜𝑘𝑎𝑠𝑖 𝑐𝑜𝑛𝑡𝑟𝑜𝑙 𝑐ℎ𝑎𝑛𝑛𝑒𝑙 =1 𝑀𝐻𝑧

20 𝑘𝐻𝑧=

106

20 × 103= 50 𝑐ℎ𝑎𝑛𝑛𝑒𝑙𝑠

Jadi jumlah voice channel = 500 − 50 = 450 𝑐ℎ𝑎𝑛𝑛𝑒𝑙𝑠 Alokasi channels untuk tiap sel apabila :

a. 𝐾 = 3 , 450

3= 150 𝑣𝑜𝑖𝑐𝑒 𝑐ℎ𝑎𝑛𝑛𝑒𝑙𝑠 untuk tiap sel dan

50

3≈ 17 control channels untuk 2 sel kemudian 1 sel

yang lain hanya punya 16 control channels.

Jawaban Soal 1 (cont)

b. 𝐾 = 4 , 450

4≈ 113 𝑣𝑜𝑖𝑐𝑒 𝑐ℎ𝑎𝑛𝑛𝑒𝑙𝑠 untuk 2 sel dan

112 voice channels untuk 2 sel lainnya dan

50

4≈ 13 control channel untuk 2 sel kemudian

2 sel yang lain hanya punya 12 control channels.

c. 𝐾 = 7 ?

Bagaimana kalau sistem yang digunakan adalah TDD ?

Basic Channels

Channel Assignment : Static Pemberian Channel untuk service demand yang datang terbatas hanya pada channel –channel yang sudah disediakan saja.

Bila Channel yang tersedia habis ? Blocking/drop packet

Solusi ?

Channel Borrowing Meminjam channel yang tidak terpakai oleh

adjacent cell, asalkan tidak mengganggu performansi adjacent cell tersebut

X

Z

Y 2

1 Cell 3

Donor Cell for Sector X

• A service initiated in the sector X of cell 3

can borrow a channel from adjacent cells 1

or 2. Cell Splitting

FREE SPACE PATHLOSS

𝑃𝑟= Received Signal Power

𝑃𝑡= Transmit Signal Power

𝐺𝑙= The product of the transmit and receive

antenna field radiation patterns in the LOS direction

𝜆= Wavelength of frequency (𝜆 = 𝑐/𝑓, where 𝑐 = 3 × 108 𝑚/𝑠

𝑑 = distance between transmitter and receiver

or

𝐺𝑙(ANTENNA DIRECTIVITY)

Example Problem

Consider an indoor wireless LAN with 𝑓𝑐 = 2400 MHz, cells of radius 10 m , and nondirectional antennas. Under the free-space path loss model, what transmit power is required at the access point such that all terminals within the cell receive a minimum power of 10 µW. How does this change if the system frequency is 5 GHz?

CIR

𝐶

𝐼=

𝑃𝑐𝑎𝑟𝑟𝑖𝑒𝑟

𝑃𝑖𝑛𝑡−𝑁𝑁𝑖=1

Dimana :

𝑃𝑐𝑎𝑟𝑟𝑖𝑒𝑟= Daya Sinyal yang diterima user dari cell serving

𝑁 = jumlah cell peng-interferensi

𝑃𝑖𝑛𝑡−𝑁 = Daya yang dirasakan oleh user di cakupan cell serving dari cell penginterferensi ke 𝑁

CINR VS SINR VS Eb/No

C/N Ratio (CNR) stands for Carrier to Noise Ratio. It is measured after modulation.

S/N Ratio (SNR) stands for Signal to Noise Ratio. It is measured before modulation.

𝑬𝒃/𝑵𝟎 = 𝑆𝑁𝑅 ×𝐵𝑊

𝑅𝑏

SOAL

Bila suatu transmitter RF seluler 1800 MHz dengan N ( Jumlah Cell Peng-Interferensi ) adalah

6, K = 3, 𝑃𝑇𝑋 = 48 𝑑𝐵𝑚, anggap 𝐺𝑙 = 1 , jari-

jari sel = 1 km, maka hitunglah a) D ! b) CIR apabila user berada di R dari 𝐵𝑆𝑠𝑒𝑟𝑣𝑖𝑛𝑔 !

REASONS FOR A HANDOFF TO BE CONDUCTED

1. To avoid call termination when the phone is moving away from the area covered by one cell and entering the area covered by another cell.

2. When the capacity for connecting new calls of a given cell is used up.

3. When there is interference in the channels due to the different phones using the same channel in different cells.

4. When the user behaviors change

5. Etc

HANDOFF PRIORITIZATION

Guard Channels: Guard channels improve the probability of successful handoffs by reserving a fixed or dynamically adjustable number of channels exclusively for handoffs. An adaptive number of guard channels can help reduce this problem.

Queuing of Handoff: Queuing is a way of delaying

handoff. The MSC queues the handoff requests instead of denying access if the candidate BS is busy. The probability of a successful handoff can be improved by queuing handoff requests at the cost of increased new call blocking probability and a decrease in the ratio of carried-to-admitted traffic since new calls are not assigned a channel until all the handoff requests in the queue are served.

HANDOFFS PROTOCOL Network-controlled handoff (NCHO) is a centralized handoff protocol, in which the network makes handoff decision based on measurements of the signal quality of mobile station (MS) at a number of based stations (BS). Sometimes the network sets up a bridge connection between the old and new BSs and thus minimizes the duration of handoff. This type of handoff is not suitable for a rapidly changing environment and a high density of users due to the associated delay. Mobile-assisted handoff (MAHO) A MAHO protocol distributes the handoff decision process. The MS makes measurements, and the BSC makes decisions.

HANDOFFS PROTOCOL Soft handoff (SHO)

is a “make before break” connection. SHO is often used in conjunction with MAHO. Rather than immediately terminating the connection between a MS and a BS, the connection to the old BS is not broken until a connection to the new BS is made.

Mobile-controlled handoff (MCHO)

The MS is completely in control of the handoff process. This type of hand off has a short reaction time and is suitable for microcellular systems. A MS keeps on measuring signal strength from all the surround base stations. If the MS find that there is a new BS who has a stronger signal than that of an old BS, it may consider to handoff from the old BS to the new BS given a certain signal threshold is reached.

Handoff/Handover

Peristiwa perpindahan kanal dari UE tanpa :

Terjadinya pemutusan hubungan

Melalui campur tangan oleh user (bukan UE)

Handoff = istilah Amerika

Handover = istilah Eropa

Handoff Default : Handoff request > Service Initiation Request

Syarat handoff : - Harus selalu berhasil - Harus tidak sering

Handoff threshold (∆): terlalu besar terlalu sering handoff terlalu kecil beban pemrosesan dan daya di BS maupun di user

∆= 𝑃𝑟−𝑕𝑎𝑛𝑑𝑜𝑓𝑓 − 𝑃𝑟−𝑚𝑖𝑛𝑖𝑚𝑢𝑚

HANDOFF PARAMETERS

∆= 𝑃𝑟 𝑕𝑎𝑛𝑑𝑜𝑓𝑓 − 𝑃𝑟 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑢𝑠𝑎𝑏𝑙𝑒

if ∆ is too big then ?

too much handoff occured, could conduct ping-pong effect

if ∆ is too small then?

Prone to handover failure

Relative signal strength

Handover chooses the strongest received base station at all times. The decision is based on an averaged measurement of the received signal.

(MORE) HANDOFF PARAMETERS

Relative signal strength with threshold

allows a user to hand over only if the current signal is sufficiently weak (less than a threshold) and the other is the stronger of the two. The effect of the threshold depends on its value


Relative signal strength with hysteresis

allows a user to hand over only if the new base station is sufficiently stronger (by a hysteresis margin) than the current one. In this case the handover will occur at point C. This technique prevents the so-called ping-pong effect


Relative signal strength with hysteresis and threshold

hands a user over to a new base only if the current signal level drops below a threshold and the target base station is stronger than the current one by a given hysteresis margin. In Figure, the handover will occur at point C if the threshold is either TI or T2, and will occur at point D if the threshold is T3


HANDOVER EVENTS

LTE measurement report triggering A1 Serving becomes better than threshold A2 Serving becomes worse than threshold A3 Neighbour becomes offset better than PCell A4 Neighbour becomes better than threshold A5 PCell becomes worse than threshold1 and neighbour becomes better than threshold2 A6 Neighbour becomes offset better than SCell C1 CSI-RS resource becomes better than threshold C2 CSI-RS resource becomes offset better than reference CSI- RS resource B1 Inter RAT neighbour becomes better than threshold B2 PCell becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2

HANDOVER EVENTS EXAMPLE : A1

CO-CHANNEL INTERFERENCE

Konsep Umum Model Area

Grafik Warna Hijau : Menunjukkan tren kekuatan

sinyal terima (Received

Signal Strength

Indicator/RSSI) berbanding

dengan jarak pada saat drive test Grafik Warna Merah : Menunjukkan hasil prediksi

Okumura-Hatta untuk jarak yang sama

Input-input yang biasa digunakan : • Frekuensi • Jarak antara Tx dan Rx • Jarak efektif antara MS dan BS • Rata-rata ketinggian kontour bumi • Marjin loss morfologi (urban,

suburban, rural )

Teknik Statistik Konsep Statistik Distribusi

• Nilai median suatu RSSI dianggap sebagai nilai RSSI yang paling sering muncul pada tiap suatu jarak dari cell, nilai RSSI yang sebenarnya bisa lebih tinggi atau lebih rendah.

• 𝑀 = nilai median dari keseluruhan data RSSI yang telah terobservasi

• 𝜎 = nilai deviasi standar dari keseluruhan data RSSI yang telah terobservasi

• 𝑀 dan 𝜎 diaplikasikan untuk menemukan probabilitas untuk menerima sembarang

level sinyal pada suatu jarak tertentu

LINK BUDGET

NOISE FIGURE

Example Problem :

𝑆𝐼𝑁𝑅 = 43 + 18 − 0 − 0.5 + 0 − 3

− 10

× log 1.38 × 10−20𝑚𝑊𝑠

𝐾× 27 + 273 𝐾 × 5 × 106

− 7 − 12 − 5 − 10 − 120 = 10.34 𝑑𝐵

Example Problem 2 Sebuah operator X ingin mendirikan satu tower Base Station di suatu kota kecil, dari parameter-parameter link budget yang telah dianalisa didapat data seperti dalam tabel berikut ini :

Parameter Link Budget Nilai Satuan

Daya Transmit BS 501 mWatt

Gain BS 18 dB

Loss kabel feeder 3 dB

loss instalasi TMA 0.5 dB

Gain Antenna UE 3 dB

Loss tubuh user 3 dB

Noise thermal -179 dB

UE Noise Figure 3 dB

SINR -5 dB

System Bandwidth 37 dB

Penetration Loss 9 dB

Fading Margin 4 dB

Interference Margin 10 dB

apabila frekuensi yang digunakan oleh teknologi seluler BS tersebut adalah 755 MHz, rata-rata tinggi efektif user adalah 1.6 meter dan jarak maksimal pancaran BS yang diinginkan adalah 1500 meter maka berapa meter-kah tinggi tower pemancar yang harus dibangun ? (gunakan Model Okumura-Hatta)

Cell Edge (Tepi Sel) Area Availability and Probability of Service

• Tentu saja Probability of Service yang paling baik adalah yang paling dekat dengan BS, dan akan semakin berkurang seiring dengan bertambahnya jarak antara MS dan BS

• Untuk probabilitas lokasi ada di dalam sel sebesar 90%, maka probabilitas akan menjadi 75% pada tepi sel.

• Model ini mendekati kebenaran apabila variasi path loss terdistribusi secara lognormal pada nilai median prediksi, seperti di environment mobile comm

• 90%/75% biasa digunakan sebagai sasaran coverage pada wireless

Contoh soal : Desainlah suatu sel yang bisa mengirimkan setidaknya -95 dBm ke 75% lokasi yang ada di sekitar tepi sel (ini akan menghadirkan cakupan 90% dari keseluruhan lokasi di dalam sel tersebut), diasumsikan deviasi standar 𝜎 sebesar 10 dB Jawab : Dari gambar Distribusi Normal di samping Atau dengan menggunakan tabel distribusi normal kita dapatkan untuk 0.75 0.675𝜎 Sehingga :

−95 𝑑𝐵𝑚 + 0.675 × 10 𝑑𝐵 = −88 𝑑𝐵𝑚

Jadi sistem harus bisa menghasilkan sinyal median sebesar -88 dBm

CONTOH SOAL

GRAFIK DAN TABEL DISTRIBUSI NORMAL

KARAKTERISASI STATISTIK BUILDING PENETRATION

Teknik statistik sangat berguna untuk kasus yang sulit untuk dikarakteristikkan - Banyak parameter, variabel dan kompleks Untuk building kita menggunakan perhitungan indoor dan outdoor pathloss, maka diperlukan : • Nilai median yang telah

disampling/diestimasikan • penentuan distribusi statistik • Perkiraan dan pengukuran deviasi

standar • Tambahan margin di link budget untuk

memberikan offset terhadap loss

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