Qualcomm Advances Sidelink Technology: Testing Demonstrates Extended Range and Non-Line-Of-sight Capabilities

Sidelink, formally designated as device-to-device (D2D) communication in the 3GPP specification framework, enables direct communication between user equipment without intermediation through cellular infrastructure.

At Critical Communications World this week, Qualcomm has announced significant progress in 5G sidelink technology development, demonstrating device-to-device connectivity achievements that extend the operational envelope for direct communication in scenarios where network infrastructure is unavailable or compromised. The company has publicly released test results from field trials conducted in Ireland and Montana, presenting technical data that reflects advancing capability maturity in a technology increasingly recognised as critical for public safety, emergency response, and mission-critical communications.

SIDELINK FUNDAMENTALS AND OPERATIONAL SIGNIFICANCE

Sidelink, formally designated as device-to-device (D2D) communication in the 3GPP specification framework, enables direct communication between user equipment without intermediation through cellular infrastructure. For critical communications operators, this capability represents a fundamental enhancement to network resilience and operational continuity, particularly in scenarios where cell tower failure, congestion, or deliberate network denial compromises conventional cellular pathways.

The technology operates across multiple frequency bands allocated by regulatory authorities globally, with harmonisation efforts ongoing to establish consistent spectrum availability across regional markets. Current development focuses on two primary frequency allocations: the 5.4 GHz band and the 1.7 GHz band, with additional consideration of lower-frequency allocations in certain jurisdictions where propagation characteristics support extended range requirements.

SPECTRUM CONSIDERATIONS AND REGIONAL HARMONISATION

Qualcomm representatives have indicated that lower frequency bands, particularly 700 MHz spectrum where available in European markets, present advantageous propagation characteristics compared to higher-frequency allocations. The company noted that frequency diversity remains necessary across European Union member states, with harmonised allocations typically comprising discrete spectrum blocks of 28 or 68 MHz rather than continuous wider allocations. This fragmentation reflects the complex regulatory landscape across Europe, where national spectrum assignments must accommodate existing licensed users and cross-border coordination requirements.

The approach to harmonisation mirrors established 5G methodologies, with the 5.4 GHz and 1.7 GHz allocations serving as primary focus areas for international standardisation. This strategy enables device manufacturers to develop multiband-capable modules that support operational deployment across multiple regulatory jurisdictions without substantial re-engineering or certification delays.

FIELD TRIAL RESULTS AND TECHNICAL PERFORMANCE

Qualcomm's test programme, executed in both rural Irish environments and Montana terrain, yielded performance data across two operational scenarios: unidirectional device-to-device communication and multi-hop relay configurations. Testing utilised the N77 frequency band allocation, designated for 3.7–3.8 GHz operation in certain markets.

In direct device-to-device communication under line-of-sight conditions, the test programme achieved 1.7-kilometre range—a substantially extended operational envelope compared to earlier-generation sidelink implementations. When the test architecture expanded to incorporate a four-device relay topology, range extended to three kilometres under non-line-of-sight conditions within densely wooded forest terrain. This configuration maintained communication paths despite absence of direct visual connectivity between terminal endpoints, demonstrating relay functionality across intermediate devices.

The performance differential between line-of-sight and non-line-of-sight scenarios reflects established electromagnetic propagation characteristics at these frequency bands. The achievement of three-kilometre non-line-of-sight range through relay architecture represents technically significant capability, particularly for public safety applications where operational areas frequently include terrain features, structures, or vegetation that obstruct direct propagation pathways.

SYNCHRONISATION CHALLENGES AND EMERGING SOLUTIONS

Current sidelink implementations require external synchronisation references for reliable operation, with present test configurations dependent upon GPS positioning and timing signals. This dependency presents operational constraints in underground, indoor, and enclosed environments where GPS signal availability is degraded or absent—precisely the scenarios most critical for emergency response operations, tunnelling infrastructure, mining operations, and underground transportation systems.

Qualcomm has identified this limitation and is developing SLSS (SideLink Sync), a self-organising synchronisation capability that enables independent device-to-device time synchronisation without external reference dependence. Under this architecture, the device maintaining the most recent connection to either network infrastructure or external timing sources assumes responsibility for establishing and maintaining the synchronisation reference, with other connected devices deriving timing from this master device.

This architectural approach fundamentally changes operational envelope. When SLSS deployment reaches production maturity, sidelink communication capability will extend into indoor environments, underground facilities, and other GPS-denied scenarios—precisely the operational domains that present maximum value for critical communications users. Emergency responders operating in subway systems, underground parking structures, mining facilities, or deep building interiors would retain connectivity capability when sidelink infrastructure deployment precedes or accompanies mission execution.

Qualcomm has indicated that expanded indoor and underground testing will commence in September, following completion of outdoor phase validation. The progression reflects standard development methodology, with outdoor performance characterisation providing baseline data before environmental complexity increases.

IMPLICATIONS FOR CRITICAL COMMUNICATIONS DEPLOYMENT

The advancement of sidelink technology carries substantial implications for the broader critical communications ecosystem. Public safety organisations operating TETRA, P25, and emerging narrowband 5G systems have historically relied upon dedicated spectrum allocations and purpose-built infrastructure to maintain communication capability during network failure scenarios. Sidelink technology, implemented across consumer and enterprise mobile device populations, offers a complementary capability pathway that leverages existing commercial device ubiquity rather than requiring dedicated public safety infrastructure investments.

The three-kilometre non-line-of-sight relay capability demonstrated in Qualcomm's testing exceeds the operational envelope of traditional land mobile radio systems, which typically operate in the two-kilometre range under similar terrain conditions. When indoor and underground SLSS capabilities mature, sidelink technology will address operational scenarios where conventional radio systems face technical constraints.

European regulatory frameworks governing critical communications spectrum have increasingly recognised sidelink capability as a component within broader resilience architectures. The European Electronic Communications Code mandates network resilience and continuity capability, with member states implementing national emergency access legislation. Integration of sidelink functionality into critical communications networks and devices represents a pragmatic approach to resilience augmentation that distributes connectivity across the device ecosystem rather than concentrating dependence upon centralised infrastructure.

STANDARDISATION AND ECOSYSTEM MATURATION

The 3GPP standardisation framework has progressively enhanced sidelink capability across multiple releases, with Release 16 introducing higher-power mode operation and Release 17 expanding relay functionality. The pathway toward GPS-independent synchronisation with SLSS represents a Release 18 priority, reflecting industry recognition that outdoor-only capability limitations substantially constrain operational applicability for public safety and mission-critical scenarios.

Device manufacturer implementation remains a prerequisite for widespread sidelink deployment. Handset and connected device manufacturers must allocate engineering resources and spectrum certification support to enable sidelink functionality across product lineups. The transition from laboratory demonstration to production-scale deployment typically requires eighteen to thirty-six months following initial technology validation, suggesting that widespread commercial sidelink availability will extend through 2027 and beyond.

Qualcomm's public release of field trial data and continued testing progress indicates commitment to sidelink technology maturation and commercial readiness. The company's transparent communication regarding both achievements and remaining development priorities—particularly the acknowledged dependency upon SLSS before full operational capability in challenging environments—reflects industry maturity and realistic technical progress assessment.

As sidelink technology transitions from standardisation and prototype validation toward commercial deployment, critical communications operators will require evaluation frameworks for integration pathway assessment. The technology's capacity to extend connectivity into environments where conventional systems face constraints, coupled with resilience advantages inherent in distributed device-based architecture, positions sidelink as a complementary component within integrated critical communications environments rather than a replacement for dedicated public safety systems.

Image: Courtesy of Henning Fjellet