# 5G-microwave Tracking Performance Characterization

## Summary (4 min read)

### 1 INTRODUCTION

- Today, the world is crowded with communication devices and radio signals which, despite not being designed for navigation, still carry a certain degree of information for location purposes.
- In the recent years, LTE signals have been regarded with interest for navigation.
- Once the CIR is estimated, the time of arrival estimate can be obtained.
- 5G sub-6 GHz signals have high central frequency (3.5 GHz) and large bandwidth (up to 100 MHz) compared to LTE signals (e.g. carrier frequency 2.8 GHz, bandwidth 20 MHz), therefore they offer potentially increased tracking performance, while they can be associated with a signal coverage that is comparable with LTE.
- The signal architecture is described with focus on ranging signal components being compared and discussed.

### 2.1 OFDM signal structure

- Orthogonal frequency division multiplexing is a multicarrier transmission scheme that divides the system bandwidth into several narrow equally spaced sub-bands, referred to as subcarriers.
- Lastly, subcarriers have separate modulation schemes that can be adapted to the frequency channel variations in flexible manner, or even muted.
- The encoding operation that maps individual blocks of data symbols to OFDM symbols is the inverse fast Fourier transform (IFFT).
- Note that the FFT is an efficient processing unit.
- As subcarrier spacing meets the inverse of symbol duration, an increase in the total number of subcarriers under the same bandwidth translates into a longer symbol duration and, therefore, a more robust multipath transmission.

### Baseband channel model

- Since the subcarriers are narrowband, the channel impulse response is assumed to be constant over the 𝑖-th transmitted symbol duration ∆𝑠′ .
- 𝑁𝑡 is the number of samples per symbol including the cyclic prefix.
- The equation above becomes much reduced under the assumption of timing and/or frequency perfectly synchronized, which holds if the residual errors 𝛾 and/or 𝜖 are nulls.

### 2.2 Correlation with an OFDM signal over the pilot subcarriers

- In OFDM, reference data symbols known as pilots are transmitted at specific times and frequencies.
- Usually, pilot subcarriers are spaced with regular interval across subcarriers, i.e., 1 subcarrier out of ∆𝑝𝑖 is a pilot subcarrier.
- 𝑁𝑔 is the first pilot index for the 𝑖-th symbol;.
- Note that the CIR estimate is the convolution of the actual CIR by a sinc function.

### 2.3 OFDM signal acquisition

- Let us consider the propagation environment as an average white gaussian noise channel (AWGN).
- Let us denote with 𝜎2 the variance of the filtered AWGN.
- After the CIR estimation, the matching pursuit (MP) algorithm [5] can be performed to obtain the delay estimates of each multipath component.

### 2.4 OFDM signal tracking

- The estimation accuracy of the signal delay can be improved using a delay-locked loop which includes a discrimination function and a loop filter.
- It can be shown that the cross-correlation function between the received signal and the early (or late) replica is a shifted copy of the cross-correlation (11), with a positive (or negative) shift that matches the one used for the replica generation.
- The normalization factor is the derivative of the s-curve in the linear region which is around the zero-crossing and it is used to make the slope of the discriminator function equal to one in the linear region.
- The position computation has not yet been developed and it is out of the scope of the paper.

### 3 LTE AND 5G SIGNALS DESCRIPTION FOR SIGNAL APPLIED STUDY

- Third Generation Partnership Project (3GPP) specifications contribute with the global scale standardization process, which is regulated by the global telecommunication standardization sector (ITU-T) of the International Telecommunication Union (ITU).
- The ITU International Mobile Telecommunication (IMT) system include evolving standard frameworks, such as IMTAdvanced and IMT-2020 for LTE and 5G industry, respectively.

### 3.1 LTE signal structure

- The frame structure of the LTE signal is defined by the European Telecommunication Standards Institute (ETSI), a European standards organization (ESO) partner with 3GPP, in its technical specification document [9].
- The signal structure for FDD is organized in frames, sub-frames and slots, where each frame (10 ms) is divided into 10 subframes and each subframe (1 ms) is divided into 2 slots (0.5 ms).
- For normal CP, a resource block consists of 12 subcarriers interspaced with ∆𝑐=15 kHz, and 7 symbols.
- The first symbol (5.21 µs) in the resource block is longer than the regular symbol duration (4.69 µs).
- The resource grid for one subframe is showed in Figure 3.

### Frequency bands

- The European Communication Office (ECO) reported information on the licensing of mobile frequency bands for the European Conference of Postal and Telecommunications Administrations (CEPT) member countries [10].
- Network operators provide mobile service through standardized 3GPP LTE bands [11].

### Cell-specific reference signals

- Cell-specific reference signals are designed for channel estimation, which permits channel equalization and data demodulation under channel distortion conditions.
- These signals are generated by using pseudo-random generators.
- The length of these signals which are transmitted in every subframe and over the whole operating bandwidth is proportional to the maximum allowed number of resource blocks.
- In case of multiple antennas, one reference signal can be mapped in different antenna ports.
- The way with which this is ruled is signal type wise.

### Synchronization signals

- The standard [9] defines two sets of signals, the primary synchronization signals, PSSs, linked to the physical-layer cell identity, and the secondary synchronization signals, SSSs, linked to the physical-layer cell identity group.
- Five consecutive resource elements are left unused at both ends of the occupied band while the direct current (DC) component is forced with null.
- The frequency allocation for PSS and SSS is showed in Figure 4.
- The same PSS sequence is transmitted in the two slots; thus, the frame boundary cannot be detected without the half-frame uncertainty by using PSS only.
- Thus, the knowledge of location of synchronization signals translates into the knowledge of duplexing scheme and it holds the other way around.

### Physical broadcast channel

- The physical broadcast channel (PBCH) is transmitted within the central six resource blocks.
- This allows the user equipment during the synchronization process to decode PBCH and read master information block (MIB) to ultimately get system bandwidth, which is needed to detect cell-specific reference signals.

### 3.2 5G signal structure

- The incoming 5G radio access technology aims at accommodating various equipment types and users, and extremely high data rate.
- Furthermore, increasing subcarrier spacing, since implies reducing symbol duration, suits low latency communication applications.
- For the purpose of this paper the authors will consider only the normal cyclic prefix.
- Each resource block consists of 12 consecutive subcarriers over the frequency domain and one OFDM symbol over the time domain.
- Inversely, the time occupancy of one resource block decreases as a function of the numerology.

### Frequency range

- In new radio, there are two separate frequency ranges respectively called FR1 and FR2.
- Each frequency range includes a certain number of operating bands.
- The frequency range FR2 is out of the scope of the paper, therefore the authors drop the description of the signal related to this frequency range.
- In the FR1, the higher carrier frequencies are placed within the operating bands 77, 78 and 79, which all are designed for commercial deployments.

### New radio system configuration

- In new radio, the total number of subcarriers, the number of data subcarriers and the sampling frequency can be configurated using the values in Table 7, 8 for respectively numerology 0, 1.
- The signals associated to numerology 2 are not covered in the context of this paper.
- To operate the initial cell search, the primary synchronization signal, PSS, and secondary synchronization signal, SSS, as well as the physical broadcast channel, PBCH, are transmitted in the synchronization signal/PBCH (SS/PBCH) block or SS block (SSB) for simplicity.
- Subcarriers number 0 through 47 and subcarrier number 192 through 239 in OFDM symbol number 2 are assigned to PBCH.
- The subcarrier and symbol indexes used in the description are defined in relation to the SSB start.

### Simulation setup

- The one side equivalent loop filter bandwidth was set to 20 Hz, the loop update spacing was set to the time separation between pilot symbols, as in Table 2, 3, 10, and the correlator spacing was set to 1 sample; the signal structure parameters.
- They have been validated by real signals for LTE, not for 5G.

### Comparative results

- Figure 8 shows the standard deviation of the delay error estimate as a function of the signal to noise ratio for different mobile radio signals.
- The simulated signals are listed in Table 11.
- For paired numerologies, the standard deviation of delay error estimate for 5G-PBCH is 2.6 times smaller than the standard deviation of delay for 5G-xSS From N0 to N1 the standard deviation of the delay estimate is reduced by a factor of 2, due to the increase of the subcarrier spacing .
- For reference signal that consists of constant number of pilot subcarriers (all other signals) the channel bandwidth does not influence the noise variance of the discriminator function.
- Therefore, the performance indicator 𝐹𝑠𝛽 = 𝐹𝑠𝑁𝑝∆𝑝 ′ 𝑁𝑐⁄ = ∆𝑓𝑁𝑝∆𝑝 ′ (21) is independent from the channel bandwidth.

Did you find this useful? Give us your feedback

##### References

2,232 citations

1,043 citations

### Additional excerpts

...Note that different algorithms performing acquisition delay estimate there exist in literature [6] [7]....

[...]

686 citations

### Additional excerpts

...After the CIR estimation, the matching pursuit (MP) algorithm [5] can be performed to obtain the delay estimates of each multipath component....

[...]

274 citations

### Additional excerpts

...Note that different algorithms performing acquisition delay estimate there exist in literature [6] [7]....

[...]

158 citations

### Additional excerpts

...The tracking loop filter can reduce the variance of the delay error at the discriminator output by a factor of 2BlTL [8], with Bl the one-side equivalent loop filter bandwidth expressed in Hertz and Tl the loop update expressed in seconds....

[...]

##### Related Papers (5)

##### Frequently Asked Questions (2)

###### Q2. What have the authors stated for future works in "5g-microwave tracking performance characterization" ?

The validation of tracking based on PBCH signals needs to be addressed in the future work. Finally, the increase of the bandwidth due to the aggregation of multiple carrier components needs to be addressed in the future work.