Constraints for the physical layer and RF equipment » History » Version 2
AUGER, Anne sophie, 03/23/2015 04:21 PM
| 1 | 1 | AUGER, Anne sophie | h1. Constraints for the physical layer and RF equipment |
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| 2 | 1 | AUGER, Anne sophie | |
| 3 | 1 | AUGER, Anne sophie | h2. Constraints for the physical layer and RF equipment: |
| 4 | 1 | AUGER, Anne sophie | |
| 5 | 1 | AUGER, Anne sophie | |
| 6 | 2 | AUGER, Anne sophie | * Required bit rate |
| 7 | 1 | AUGER, Anne sophie | |
| 8 | 1 | AUGER, Anne sophie | |
| 9 | 2 | AUGER, Anne sophie | In order to define the bit rate required for the transmission of video streams we need some input parameters, provided in the mission statement: |
| 10 | 2 | AUGER, Anne sophie | |
| 11 | 2 | AUGER, Anne sophie | > # aspect ratio of the video : AR=1,78 |
| 12 | 2 | AUGER, Anne sophie | > # quality of the encoded video L=720p |
| 13 | 2 | AUGER, Anne sophie | > # frame cadence FPS=12 fps |
| 14 | 2 | AUGER, Anne sophie | |
| 15 | 2 | AUGER, Anne sophie | We used the following formula |
| 16 | 2 | AUGER, Anne sophie | |
| 17 | 2 | AUGER, Anne sophie | p=. Bit rate = FPS*5,0692 * L ^1,391^ /(1000*AR) |
| 18 | 2 | AUGER, Anne sophie | |
| 19 | 2 | AUGER, Anne sophie | So |
| 20 | 2 | AUGER, Anne sophie | |
| 21 | 2 | AUGER, Anne sophie | p=. *Bit rate=322 Kbps* |
| 22 | 2 | AUGER, Anne sophie | |
| 23 | 2 | AUGER, Anne sophie | As the link will allow video transmission, we will need an adapted encapsulation protocol, so we must take into account extra bits: we decide to define a bit rate of 500 kbps. |
| 24 | 2 | AUGER, Anne sophie | |
| 25 | 2 | AUGER, Anne sophie | |
| 26 | 2 | AUGER, Anne sophie | |
| 27 | 1 | AUGER, Anne sophie | From the given allocated frequency band, the following parameters are defined: |
| 28 | 1 | AUGER, Anne sophie | * f : Central frequency of the emitted signal |
| 29 | 2 | AUGER, Anne sophie | * B: Width of the allocated bandwidth |
| 30 | 1 | AUGER, Anne sophie | * EIRP: Maximum power that can be emitted in a given direction |
| 31 | 1 | AUGER, Anne sophie | |
| 32 | 1 | AUGER, Anne sophie | From the specifications, the following parameters are defined: |
| 33 | 1 | AUGER, Anne sophie | * Rb: Useful bit rate of the transmission |
| 34 | 1 | AUGER, Anne sophie | * R : Minimal distance for the transmission |
| 35 | 1 | AUGER, Anne sophie | |
| 36 | 1 | AUGER, Anne sophie | The value of these parameters constrain the parameters of the physical layer and the RF equipment for the design of the system. |
| 37 | 1 | AUGER, Anne sophie | |
| 38 | 1 | AUGER, Anne sophie | |
| 39 | 1 | AUGER, Anne sophie | h3. Physical layer: |
| 40 | 1 | AUGER, Anne sophie | |
| 41 | 1 | AUGER, Anne sophie | The study of the physical layer will be limited to the choice of the modulation, the coding and the shaping filter. We will consider a SRRC filter (Square Root Raised Cosine) for the shaping filter as it is commonly used in telecommunication systems for its good performances. |
| 42 | 1 | AUGER, Anne sophie | |
| 43 | 1 | AUGER, Anne sophie | Then, the parameters of the physical layer are: |
| 44 | 1 | AUGER, Anne sophie | * M : Modulation (M=4 : QPSK, M=8 : 8PSK etc) |
| 45 | 1 | AUGER, Anne sophie | * rho : Coding rate (rho <1) |
| 46 | 1 | AUGER, Anne sophie | * alpha : roll-off of the SRRC filter |
| 47 | 1 | AUGER, Anne sophie | |
| 48 | 1 | AUGER, Anne sophie | In fact all these parameters are linked through the spectral efficiency T of the system, which is fixed by B and Rb: |
| 49 | 1 | AUGER, Anne sophie | |
| 50 | 1 | AUGER, Anne sophie | T= cst et T= |
| 51 | 1 | AUGER, Anne sophie | |
| 52 | 1 | AUGER, Anne sophie | Then, the parameters of the physical have to comply with the following relation: |
| 53 | 1 | AUGER, Anne sophie | |
| 54 | 1 | AUGER, Anne sophie | T>cst |
| 55 | 1 | AUGER, Anne sophie | |
| 56 | 1 | AUGER, Anne sophie | |
| 57 | 1 | AUGER, Anne sophie | |
| 58 | 1 | AUGER, Anne sophie | h3. Link budget: |
| 59 | 1 | AUGER, Anne sophie | |
| 60 | 1 | AUGER, Anne sophie | Here is the expression of the link budget: |
| 61 | 1 | AUGER, Anne sophie | |
| 62 | 1 | AUGER, Anne sophie | (link budget) |
| 63 | 1 | AUGER, Anne sophie | |
| 64 | 1 | AUGER, Anne sophie | We can notice that all the parameters are already known, except: |
| 65 | 1 | AUGER, Anne sophie | * (G/T): Figure of merit of the receiver (ISAE antenna) |
| 66 | 1 | AUGER, Anne sophie | * Lmarg: Margin on the link budget to take into account all the perturbations (antenna |
| 67 | 1 | AUGER, Anne sophie | depointing, atmosphere attenuation, interferences, non-ideal demodulator …) |
| 68 | 1 | AUGER, Anne sophie | |
| 69 | 1 | AUGER, Anne sophie | Lmarg being only linked to physical parameters, we don’t have any influence on it. Then, it has to be evaluated but it is not really a parameter of the design. |
| 70 | 1 | AUGER, Anne sophie | |
| 71 | 1 | AUGER, Anne sophie | Power amplifier |
| 72 | 1 | AUGER, Anne sophie | |
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| 74 | 1 | AUGER, Anne sophie | h2. Conclusion: |
| 75 | 1 | AUGER, Anne sophie | |
| 76 | 1 | AUGER, Anne sophie | From these considerations, our aim will be to: |
| 77 | 1 | AUGER, Anne sophie | * Choose the modulation and the coding (according to the shaping filter) |
| 78 | 1 | AUGER, Anne sophie | * Compute the gain of the receiving antenna |
| 79 | 1 | AUGER, Anne sophie | * Propose some technical solution for the receiving antenna |
| 80 | 1 | AUGER, Anne sophie | |
| 81 | 1 | AUGER, Anne sophie | We will also develop tools to visualize the influence of the bandwidth, EIRP, useful bit rate and distance on the system design. |
| 82 | 1 | AUGER, Anne sophie | |
| 83 | 1 | AUGER, Anne sophie | The aircraft antenna will be considered able to fulfil the required antenna pattern, but we will not discuss about technical solutions for this antenna, as it can be really tricky. |