شرح كباين موتورولا للمهندس احمد شوقي



بسم الله الرحمن الرحيم 


انا اخوكم المهندس احمد هحاول فى البدايه اقولكم مكونات كباين موتورلا

فى البدايه فى نوعين من الكباين horizon 1 
ودى قديمه جدا ونادر لما بتلاقيها فى سيتات فى منها بس قليل اوى 
والنوع التانى اللى هو horizon 2
وده زى اللى فى الصورة وبيتكون من اللى على اليمين 
كارت اسمه h2sc
وده عباره عن البروسيسور بتاع الكابينه والكارت اللى جمبه ده
 فى الصورة بس فى الغالب بيكون كارت واحد بس فى الكابينه واللى بعده ده كارت الالارمات الداخليه بتاعت الكابينه بتظهر عليه بعد كده فى الكروت اللى بتشيل المكالمات وهى نوعين اول حاجه اسمها
gsm 900
وده زى اللى فى الصورة والنوع التانى
بيكون DCS 1800
وطبعا الاختلاف بيكون فى الباند بتاعتنا وغالبا كل نوع بيكون فى كابينه غير التانيه يعنى ال
gsm 900
فى كابينه مثلا والتانى فى كابينه غيرها فى نفس السيتوهما دول بس النوعين اللى موجودين عندنا مفيش انواع كتيره زى هواوى بعد كده فى اللى تحتهم دى فانات عشان تهوى ع الكروتوا للى على الشمال خالص دول ال
power supply
وفى حاجه اسمها circuit breaker
ودى عباره عن المفاتيح بتاعت البور بتاعت كل الكروت اللى عندنا دى يعنى اللى بتطفيها وتشغلها منهم





دى صورة لدوبلكسرات من فوق من كابينه فى الشكل ده كل راديو متوصل بدوبلكسر بس عاده مش كل راديو بيتوصل بدوبلكسر
وفى كارت اسمه HCU
وده وظيفته انه يوصل اتنين راديو على دوبلكسر واحد يعنى حاجه زى المشترك كده



horizon 2
بس هنا فى الصورة الكابينه من فوقالحاجات اللى على اليمين دى الى مكتوب عليها
tx blocks 



دى عباره عن حاجه اسمها الدوبلكسر  وده بيتوصل بيه الجمبر اللى هو جاى من الفيدر اللى جاى من الانتينا ووظيفه الدوبلكسر ده انه بيختار افضل مسار للاشاره يعنى مثلا بيشوف الراديو
وعندنا هنا اسمهم راديو بيشوف الراديو الفاضى اللى مش مشغول عشان يتحمل عليه المكالمه وبيتوصل الدوبلكسر ده
بكارت ورا كده اسمه كارت السيرف
ووظيفه الكارت ده انه بيعمل فيلتر للاشاره  بياخد الاشارة يظبطها ويبعتها تانى وبعدين بيتوصل الدوبلكسر بالرداوى بتاعتناوفى حاجه ع الشمال مكان الكارت اللى فى النص اللى فيه فتحات ده
بيكون متوصل مكانه كارته الBIB
وبيتوصل فيها كابل ال BIB
وده اللى بينقل الترافيك
بتاع الكابينه كله لل DDF


اخوكم المهندس أحمد شوقى

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CDMA / UMTS RF Interview Questions 4

1. What are the RRC states?
There are 4 RRC States: Cell_DCH, Cell_FACH, URA_PCH and Cell_PCH.

URA = UTRAN Registration Area.
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2. What are transparent mode, acknowledged mode and unacknowledged mode?
· Transparent mode corresponds to the lowest service of the RLC layer, no controls and no
detection of missing data.
· Unacknowledged mode offers the possibility of segment and concatenate of data but no
error correction or retransmission therefore no guarantee of delivery.
· Acknowledged mode offers, in addition to UM mode functions, acknowledgement of
transmission, flow control, error correction and retransmission.

3. Which layer(s) perform ciphering function?
RRC – for acknowledged mode (AM) and unacknowledged mode (UM).
MAC – for transparent mode (TM).

4. What is OVSF?
Orthogonal Variable Spreading Factor.

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5. How many OVSF code spaces are available?
· Total OVSF codes = 256.
· Reserved: 1 SF64 for S-CCPCH, 1 SF256 for CPICH, P-CCPCH, PICH and AICH each.
· Total available code space = 256 – 4 (1 SF64) – 4 (4 SF256) = 248.

6. Can code space limit the cell capacity?
Yes, cell capacity can be hard-limited by code space. Take CS-12.2k for example:
· A CS-12.2k bearer needs 1 SF128 code.
· Total available codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.
· Consider soft-handover factor of 1.8: 124 / 1.8 = 68 uers/cell.

7. Can a user have OVSF code as “1111”?
No, because “1111…” (256 times) is used by CPICH.

8. What are the symbol rates (bits per symbol) for BPSK, QPSK, 8PSK and 16QAM?
· BPSK: 
.

· QPSK:
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· 8PSK:


· 16QAM: 


9. Briefly describe UMTS frame structure.
· UMTS frame duration = 10ms.
· Each frame is divided into 15 timeslots.
· Each timeslot is divided into 2560 chips.
· Therefore 2560 chips/TS * 15 TS/frame * (1000ms/10ms) frame/sec = 3,840,000
chip/sec.

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10. What is cell selection criterion?
Cell selection is based on:
· Qmean: the average SIR of the target cell.
· Qmin: minimum required SIR.
· Pcompensation: a correction value for difference UE classes.
S = Qmean - Qmin - Pcompensation
· If S>0 then the cell is a valid candidate.
· A UE will camp on the cell with the highest S.

11. Briefly describe Capacity Management and its functions:
Capacity Management is responsible for the control of the load in the cell. It consists of 3
main functions:
· Dedicated Monitored Resource Handling: tracks utilization of critical resources of the
system.
· Admission Control: accepts/refuses admission requests based on the current load on the
dedicated monitored resources and the characteristics of the request
· Congestion Control: detects/resolves overload situations

12. What are the major 4 KPIs in propagation model tuning and typical acceptable values?
The 4 KPIs are standard deviation error, root mean square error, mean error and correlation
coefficient. The typical acceptable values are:
· Standard deviation error: the smaller the better, usually 7 to 9dB.
· Mean error: the smaller the better, usually 2 to3.
· Root mean square error: the smaller the better, usually
· Correlation coefficient: the larger the better, usually 70% to 90%.

13. What is the minimum number of bins required for a certain propagation model?
The more bins the more likely to come up with a good model. Usually a minimum of 2,000
bines is considered acceptable, but sometimes as low as 500 bins may be accepted.
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14. How many scrambling codes are there?
There are 512 scrambling codes in the downlink and 16,777,216 codes in the uplink.

15. How many scrambling code groups are there for downlink?
There are 64 code groups, each group has 8 scrambling codes.

16. Can we assign same scrambling codes to sister sectors (sectors on same site)?
No, because scrambling code on the downlink is used for cell identity. As a requirement,
scrambling codes have to maintain a safe separation to avoid interference.

17. Are scrambling codes orthogonal?
No, scrambling codes are not orthogonal since they are not synchronized at each receiver.
They are pseudo random sequences of codes.

18. Can we assign scrambling codes 1, 2 and 3 to sister sectors?
Yes.

19. In IS-95 we have a PN reuse factor (PN step size) and therefore cannot use all 512 PN
codes, why isn’t it necessary for UMTS scrambling codes?
Because IS-95 is a synchronized network, different PN codes have the same code sequence
with a time shift, therefore we need to maintain a certain PN step size to avoid multi-path
problem. For example, if two sectors in the neighborhood have a small PN separation then
signal arriving from cell A may run into the time domain of cell B, causing interference.
UMTS, on the other hand, is not a synchronized network and all scrambling codes are
mutually orthogonal so no need to maintain a step size.
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20. What are coverage thresholds in your UMTS design and why?
The coverage thresholds are based on UE sensitivity, fading and penetration loss. Assuming
UE sensitivity of -110dBm, fade margin of 5dB:
· Outdoor: -110dBm sensitivity + 5dB fade margin = -105dBm.
· In-vehicle: -110dBm + 5dB + 8dB in-vehicle penetration loss = -97dBm.
· In-building: -110dBm + 5dB + 15dB in-building penetration loss = -90dBm.

21. What is the Ec/Io target in your design?
The Ec/Io target typically is between -12 to -14dB. However, if a network is designed for
data then the Ec/Io target could go higher to around -10dB because server dominance is more
critical for a data network – since there isn’t software in the downlink.


GSM RF INTERVIEW QUESTIONS 3

1. What are TDMA frames, multiframes, superframes and hyperframes?



2. Why do we need FCCH, SCH and BCCH? 

FCCH: Identifies BCCH carrier by the carrier frequency and synchronizes with the frequency.
Synchronization Channel (SCH): Transmits information about the TDMA frame structure in a cell (e.g. frame number) and the BTS identity (Base Station Identity Code (BSIC)).
BCCH: Broadcasts some general cell information such as Location Area Identity
(LAI), maximum output power allowed in the cell and the identity of BCCH carriers for neighboring cells.
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3. Why do we need SACCH?
 Instructs the MS the transmitting power to use and gives instructions on timing advance.

4. What is the purpose of PCH and CBCH?
 Paging Channel (PCH): Transmits a paging message to indicate an incoming call or short message. The paging message contains the identity number of the mobile subscriber that the network wishes to contact.
Cell Broadcast Channel (CBCH): BS uses this logical channel to transmit short message service cell broadcast.

5. Do we keep BCCH on a hopping radio? Give the reason to support your answer.
No, BCCH is a signaling channel which must be continuously transmitted in a cell.

6. Explain the structure of a Traffic Multiframe. Why do we need SACCH and Idle bursts in a traffic multiframe?
Traffic Multiframe Structures - The 26 traffic multiframe structure is used to send information on the traffic channel. The 26 traffic multiframe structure is used to combine user data (traffic),
 slow control signaling (SACCH), and idle time period. The 12th frame (no. 13) in the 26-frame traffic channel multiframe is used by the Slow Associated Control Channel (SACCH) which carries link control information to and from the MS–BTS. Each timeslot in a cell allocated to traffic channel usage will follow this format, that is, 12 bursts of traffic, 1 burst of SACCH, 12 bursts of traffic and 1 idle.
Idle Bursts: The idle time period allows a mobile device to perform other necessary operations such as monitoring the radio signal strength level of a beacon channel from other cells. The time interval of a 26 frame traffic multiframe is 6 blocks of speech coder data (120 msec).

7. How is a FACCH formed? When is a FACCH used?
 Fast Associated Control Channel (FACCH): Transmits handover information.

8. What are bursts? Explain various types of bursts, Radio Propagation and Antennas?
Bursts
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Radio Propagation
It is how the radio propagates from the transmitter till reaching the receiver, maybe the signal encounter obstacles, Knife Edge…etc.
Wave propagation is difficult, no one can argue against that. Nevertheless, it is necessary, for example when planning mobile telephony systems, to define methods for predicting propagation in an area. Different models for estimating signal strength are used for this purpose. They might be simple expressions, suitable for rough assessments or complicated algorithms that demand considerable computation time. The simplest model for wave propagation is the free space case.
Antennas
Isotropic antenna: An isotropic antenna is a completely non-directional antenna that radiates equally in all directions. Since all practical antennas exhibit some degree of directivity, the isotropic antenna exists only as a mathematical concept. The isotropic antenna can be used as a reference to specify the gain of a practical antenna.
The gain of an antenna referenced isotropically is the ratio between the power required in the practical antenna and the power required in an isotropic antenna to achieve the same field strength in the desired direction of the measured practical antenna. The directive gain in relation to an isotropic antenna is called dBi.

Half-wave dipole antenna: A half-wave dipole antenna may also be used as a gain reference for practical antennas. The half-wave dipole is a straight conductor cut to

one-half of the electrical wavelength with the radio frequency signal fed to the middle of the conductor. Directive gain in relation to a dipole is expressed in units of “dBd”.
For a dipole and an isotropic antenna with the same input power, the energy is more concentrated in certain directions by the dipole. The difference in directive gain between the dipole and the isotropic antenna is 2.15 dB. Figure illustrates the differences in gain between the isotropic, dipole, and practical antenna. The vertical pattern (Figure) of the practical antenna is that of a directional antenna.



9. What is VSWR? Why do we need it?
Standing wave ratio (SWR) is the ratio of the amplitude of a partial standing wave at an antinode (maximum) to the amplitude at an adjacent node (minimum), in an electrical transmission line. The SWR is usually defined as a voltage ratio called the VSWR, for voltage standing wave ratio. SWR is used as an efficiency measure for transmission lines, electrical cables that conduct radio frequency signals, used for purposes such as connecting radio transmitters and receivers with their antennas, and distributing cable television signals.
A problem with transmission lines is that impedance mismatches in the cable tend to reflect the radio waves back toward the source end of the cable, preventing all the power from reaching the destination end. SWR measures the relative size of these reflections. An ideal transmission line would have an SWR of 1:1, with all the power reaching the destination and no reflected power. An infinite SWR represents complete reflection, with all the power reflected back down the cable. The SWR of a transmission line is measured with an instrument called an SWR meter, and checking the SWR is a standard part of installing and maintaining transmission lines.
The voltage standing wave ratio is then equal to:
Where (ρ) is the magnitude of reflection coefficient.
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10. What do you mean by EIRP?
Effective isotropic radiated power (EIRP) is the amount of power that a theoretical isotropic antenna (that evenly distributes power in all directions) would emit to produce the peak power density observed in the direction of maximum antenna gain. EIRP can take into account the losses in transmission line and connectors and includes the gain of the antenna. The EIRP is often stated in terms of decibels over a reference power emitted by an isotropic radiator with equivalent signal strength. The EIRP allows comparisons between different emitters regardless of type, size or form.
EIRP = P_T - L_c + G_a
where \scriptstyle EIRP and \scriptstyle P_T (output power of transmitter) are in dBm, cable losses (\scriptstyle L_c) is in dB, and antenna gain (\scriptstyle G_a) is expressed in dBi, relative to a (theoretical) isotropic reference antenna.

11. What is Polarization? What are the types of polarization?
The polarization indicates the plane in which the wave is vibrating. The polarization plane is taken to be that of the electric component.
Vertical and horizontal are the simplest forms of polarization, and they both fall into a category known as linear polarization. However, it is also possible to use circular polarization. This has a number of benefits in areas such as satellite applications, where it helps to overcome the effects of propagation anomalies, ground reflections and the spin that occur on many satellites. Circular polarization is a little more difficult to visualize than linear polarization; however, it can be imagined by visualizing a signal propagating from an antenna that is rotating. Another form of polarization is known as elliptical polarization.

12. What is fading?
Fading is the variation of the received signal with time, it occurs due to propagation distance.
Short term (fast) fading: caused by multipath propagation.
Long term (slow) fading: caused by shadowing.

13. What is Rayleigh Fading?
Rayleigh fading is a reasonable model when there are many objects in the environment that scatter the radio signal before it arrives at the receiver.
Rayleigh fading models assume that the magnitude of a signal that has passed through such a communications channel will vary randomly, or fade, according to a Rayleigh distribution the radial component of the sum of two uncorrelated Gaussian random variables.
Rayleigh fading is most applicable when there is no dominant propagation along a line of sight between the transmitter and receiver. If there is a dominant line of sight, Rician fading may be more applicable.
55. What is multipath fading?
Multipath fading is receiving multiple copies of the signal at receiver due to reflections. The copies reach the receiver with different phases, so summation either constructive or destructive. This affects the quality of received signal in terms of BER.

14. What is multipath fading?
Multipath fading is receiving multiple copies of the signal at receiver due to reflections. The copies reach the receiver with different phases, so summation either constructive or destructive. This affects the quality of received signal in terms of BER.

15. How can we minimize multipath fading?
By using channel equalizer.

16. What are the different types of diversity?
A. Space Diversity.

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The distance between the antenna must be such relationships in the two-antenna signal, which is low. Relationships are the equations that describe the statistical limits of the signal. In practice, the distance should be a few meters. At 900 MHz is possible strengthening of 3 dB, used a distance of 5 to 6 meters between the two antenna .. At 1800 MHz the distance would be minimized because a smaller wavelength.

B. Polarization Diversity.
Antenna Dual Polarization is: an antenna device with 2 rows with the same physical unit. Both lines can be arranged and directed in various ways during the second plan of polarization have the same performance by strengthening and examples of radiation. Two forms are commonly used together, namely: Vertical and Horizontal rows and rows in the slope of 45 °.

C. Time Diversity.
D. Frequency Diversity

17. Explain various types of Antenna Diversity?
Antenna diversity increases the received signal strength by taking advantage of the natural properties of radio waves. There are two primary diverstiy methods: space diversity and polarization diversity.
Space Diversity: Increased received signal strength at the BTS may be achieved by mounting two receiver antennae instead of one. If the two Rx antennae are physically separated, the probability that both of them are affected by a deep fading dip at the
same time is low. At 900 MHz, it is possible to gain about 3 dB with a distance of five to six meters between the antennae. At 1800 MHz the distance can be shortened because of its decreased wavelength.
By choosing the best of each signal, the impact of fading can be reduced. Space diversity offers slightly better antenna gain than polarization diversity, but requires more space.
Polarization Diversity: With polarization diversity the two space diversity antennae are replaced by one dual polarized antenna. This antenna has normal size but contains two differently polarized antenna arrays. The most common types are vertical/horizontal arrays and arrays in 45 degree slant orientation. The two arrays are connected to the respective Rx branches in the BTS. The two arrays can also be used as combined Tx/Rx antennas. For most applications, the difference between the diversity gain for space diversity and polarization diversity is negligible, but polarization diversity reduces the space required for antenna.
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18. Explain Frequency Diversity.
By using frequency hopping sequence.

19. Explain Time Diversity.
By using code interleave technology.