5GNR Reference Signals Measurement

In 5G new  radio (NR) system, reference signal   measurement are used to perform cell selection, cell reselection and handover etc.  Reference Signal (RS) measurements are further classified into three measurement parameters as given

In 5G new  radio (NR) system, reference signal   measurement are used to perform cell selection, cell reselection and handover etc.  Reference Signal (RS) measurements are further classified into three measurement parameters as given below: 

  •        Reference Signal Received Power (RSRP)
  •        Received Signal Strength Indicator (RSSI)
  •        Reference Signal Received Quality (RSRQ)

 These measurements (i.e. RSRP, RSRQ, RSSI) are included in the RRC Information Elements (IEs) carries. 

Received Signal Strength Indicator (RSSI):

RSSI is defined as  the total received wide-band power measured over entire bandwidth by UE. RSSI is not reported to eNodeB. The RSSI is used in the calculation of RSRQ in LTE system. RSSI is also a power and its measurement unit is dBm

 RSSI = Serving Cell Power + Neighbour Co-Channel Cells Power + Thermal Noise

 Under full Load condition the  RSRP (dBm)= RSSI – 10*log (12*N)

where N  represents number of resource block. 

 

 

 

 

 

 

 

Bandwidth

1.4 mHz

3 mHz

5 mHz

10 mHz

15 mHz

20 mHz

No. of Resource block(N)

6

15

25

50

75

100

Scaling Factor:- 1o log (12N)

18.57

22.55

24.77

27.78

29.54

30.72

 

 

By using above equation RSSI can be calculated as:

If RSRP is -60 dBm and the cell is fully loaded (20MHz) and the UE is experiencing 10dBm power from a Neighbour cell operating at same frequency RSSI measured -60 dBm + 30.72 dBm +10 dBm = -19.98 dBm.

 So from the above calculation it can be concluded that if UE is seeing only one cell then there is relation between RSRP and can be directly scaled by the factor for particular bandwidth given in the table1, but UE start seeing more signal on the same frequency from other cell then RSSI value become even better.

 Reference Signal Received Power(RSRP):

RSRP is the linear average of reference signal power (in Watts) measured over a specified bandwidth (in number of REs). It is very similar to CPICH RSCP in WCDMA. It is applicable while UE in different RRC states i.e. RRC_IDLE intra-frequency, RRC_IDLE inter-frequency, RRC_CONNECTED intra-frequency, RRC_CONNECTED inter-frequency.

 

RP(Integer)

From RSRP Value (dBm)

To RSRP Value (dBm)

00

 

-140 dBm

01

-140 dBm

-139 dBm

02

-139 dBm

-138 dBm

03

-138 dBm

-137 dBm

04

-137 dBm

-136 dBm

05

-135 dBm

-134 dBm

06

-134 dBm

-133 dBm

07

-133 dBm

-132 dBm

08

-132 dBm

-131 dBm

09

-131 dBm

-130 dBm

10

-130 dBm

-129 dBm

11

-129 dBm

-128 dBm

12

-128 dBm

-127 dBm

13

-127 dBm

-126 dBm

14

-126 dBm

-125 dBm

15

-125 dBm

-124 dBm

16

-124 dBm

-123 dBm

17

-123 dBm

-122 dBm

18

-122 dBm

-121 dBm

19

-121 dBm

-120 dBm

20

-120 dBm

-119 dBm

21

-119 dBm

-118 dBm

22

-118 dBm

-117 dBm

23

-117 dBm

-116 dBm

24

-116 dBm

-115 dBm

25

-115 dBm

-114 dBm

26

-114 dBm

-113 dBm

27

-113 dBm

-112 dBm

28

-112 dBm

-111 dBm

29

-111 dBm

-110 dBm

30

-110 dBm

-109 dBm

31

-109 dBm

-108 dBm

32

-108 dBm

-107 dBm

33

-107 dBm

-106 dBm

34

-106 dBm

-105 dBm

35

-105 dBm

-104 dBm

36

-104 dBm

-103 dBm

37

-103 dBm

-102 dBm

38

-102 dBm

-101 dBm

39

-101 dBm

-100 dBm

40

-100 dBm

-99 dBm

41

-99 dBm

-98 dBm

42

-98 dBm

-97 dBm

43

-97 dBm

-96 dBm

44

-96 dBm

-95 dBm

45

-95 dBm

-94 dBm

46

-94 dBm

-93 dBm

47

-93 dBm

-92 dBm

48

-92 dBm

-91 dBm

49

-91 dBm

-90 dBm

50

-90 dBm

-89 dBm

51

-89 dBm

-88 dBm

52

-88 dBm

-87 dBm

53

-87 dBm

-86 dBm

54

-86 dBm

-85 dBm

55

-85 dBm

-84 dBm

56

-84 dBm

-83 dBm

57

-83 dBm

-82 dBm

58

-82 dBm

-81 dBm

59

-81 dBm

-80 dBm

60

-80 dBm

-79 dBm

61

-79 dBm

-78 dBm

62

-78 dBm

-77 dBm

63

-77 dBm

-76 dBm

64

-76 dBm

-75 dBm

65

-75 dBm

-74 dBm

66

-74 dBm

-73 dBm

67

-73 dBm

-72 dBm

68

-72 dBm

-71 dBm

69

-71 dBm

-70 dBm

70

-70 dBm

-69 dBm

71

-69 dBm

-68 dBm

72

-68 dBm

-67 dBm

73

-67 dBm

-66 dBm

74

-66 dBm

-65 dBm

75

-65 dBm

-64 dBm

76

-64 dBm

-63 dBm

77

-63 dBm

-62 dBm

78

-62 dBm

-61 dBm

79

-61 dBm

-60 dBm

80

-60 dBm

-59 dBm

81

-59 dBm

-58 dBm

82

-58 dBm

-57 dBm

83

-57 dBm

-56 dBm

84

-56 dBm

-55 dBm

85

-55 dBm

-54 dBm

86

-54 dBm

-53 dBm

87

-53 dBm

-52 dBm

88

-52 dBm

-51 dBm

89

-51 dBm

-50 dBm

90

-50 dBm

-49 dBm

91

-49 dBm

-48 dBm

92

-48 dBm

-47 dBm

93

-47 dBm

-46 dBm

94

-46 dBm

-45dBm

95

-45dBm

-44 dBm

96

-45dBm 

-44 dBm

97

-44 dBm

 

  Practical Example of RSRP:

 Let’s consider a single atnenna system and say the Reference Signal Transmitted power is about 12 dBm. A UE is located somewhere in the cell experiencing a path loss of 100 dB. Then the RSRP measured by UE should be 12-100 = -88 dBm , When we compare -88dBm value in then Table 2 it is corresponding to RSRP Integer value 52 so UE can report RSRP=52 in the measurement report.

 Normally, when anyone see the UE logs measurement report ,it contained the RSRP integer value, the quick way to find our absolute RSRP value in dBm is simply subtract the integer value from -140 .Let’s take an example Integer RSRP value is 45 then corresponding RSRP dBm = -140 + 45 = -95 dBm.

 RSRQ:

RSRQ is th Reference Signal Received Quality and it can be defined using following equation:

 RSRQ= (N* RSRP)/RSSI

As per the definition of RSSI, It is wide band power including signal power from serving cell, co-channel neighbour cell, interference from other cell interference and noise, in similar word one can say that RSRQ define the purity of Reference Signal (RS) across the system bandwidth. RSRQ is a calculated value from RSRP and RSSI is measure of signal and interference. As RSRQ is a ration of two signal powers with same  same unit i.e. dBm so RSRQ uses dB as a measurement unit.

 Similar to RSRP , UE reported an integer value to eNodeB and its range is from 0 to 34 (Table 3). 3GPP has provided a table shown below, by using this table the integer value can be translated to a range of RSRP value in dB.

 The best value of RSRP is about -3 dB and worst value can be -19.5dB. 

Reported RSRQ(Integer)

From RSRQ Value(dB)

To RSRQ Value(dB)

00

 

-19.5 dB

01

-19.5 dB

-19 dB

02

-19 dB

-18.5 dB

03

-18.5 dB

-18.0 dB

04

-18.0 dB

-17.5 dB

05

-17.5 dB

-17.0 dB

06

-17.0 dB

-16.5 dB

07

-16.5 dB

-16.0 dB

08

-16.0 dB

-15.5 dB 

09

-15.5 dB

-15.0 dB

10

-15.0 dB

-14.5 dB

11

-14.5 dB

-14.0 dB

12

-14.0 dB

-13.5 dB

13

-13. 5 dB 

-13.0 dB

14

-13.0 dB

-12.5 dB

15

-12.5 dB

-12.0 dB

16

-12.0 dB

-11.5 dB

17

-11.5 dB

-11.0 dB

18

-11.0 dB

-10.5 dB

19

-10.5 dB

-10.0 dB

20

-10.0 dB

-9.5 dB 

21

-9.5 dB

-9.0 dB

22

-9.0 dB

-8.5 dB

23

-8.5 dB

-8.0 dB

24

-8.0 dB

-7.5 dB

25

-7.5 dB

-7.0 dB

26

-7.0 dB

-6.5 dB

27

-6.5 dB

-6.0 dB

28

-6.0 dB

-5.5 dB

29

-5.5 dB

-5.0 dB

30

-5.0 dB

-4.5 dB

31

-4.5 dB

-4.0 dB

32

-4.0 dB

-3.5 dB

33

-3.5 dB

-3.0 dB

34

-3.0 dB

 

So, when there is no traffic, and assuming only the reference symbols are transmitted (there are 2 of them within the same symbol of a resource block) from a single Tx antenna then the RSSI is generated by only the 2 reference symbols so the result becomes:

 RSRQ = N / 2N = -3 dB for 1Tx

RSRQ = -6 dB for 2Tx

If all resource elements are active and are transmitted with equal power, then

 RSRQ = N / 12N = -10.8 dB for 1Tx

RSRQ = N / 20N = -13 dB for 2Tx

(because RSRP is measured over 1 resource element and RSSI per resource block is measured over 12 resource elements).

 Reference: TS 36.133

                  TS 36.304